While string theory (ST) is based on LS, this result was interpreted by Motl as a confirmation of ST, although in fact it confirms the validity of one of string theory postulates only. Although gamma ray dispersion was considered as one of main tests of quantum gravity theories and the picture bellow was presented in many places, LQG theory in its current state of development has nothing to say very much to this result, because it maintains LS in 3D in the same way, like string theory, as Lee Smolin explained. This picture is a snapshot of article in Scientific American, 59: "Atoms of space and time", which is definitelly worth reading by itself - but it contains desinformation, concerning LQG predictions.
Phenomenological explanation of this controversy is simple in AWT and it's based on the fact, LS is valid only for strictly 3D space, whereas cosmic space is filled by gravitons expanded into gravitational waves during inflation, i.e. tiny density fluctuations responsible for cosmic microwave background (CMB). Therefore cosmic space isn't completely "flat" and it contains "traces of higher dimensions". While LS is indeed valid for all higher hyperspaces, their projection into 3D space isn't invariant with respect to LS anymore. From AWT follows, only microwaves can propagate through vacuum like harmonic wave, thus fulfilling LS at long distances, while longer waves are propagating like tachyons and shorter waves are always composed of photons, which are propagating by subluminal speed. This dispersion can be observed in GZK limit for gamma ray photons and it manifests by delay for gamma ray photons during weak (short distance) gamma ray bursts, like MKN501 event, observed last year. In accordance with this explanation, the dispersion of more close gamma ray flashes is usually much more pronounced, then at the case of these remote ones.
As a pronounced example of light dispersion during spreading through compactified gradient can can serve Hawking radiation of black holes, which can be interpreted like light escaping from glass sphere. Long wavelengths and gravitational waves can penetrate it freely, whereas shorter wavelengths are reflected back again by total reflection mechanism
The reason, why GRB090510 burst (and some others, like GRB 080916C from September 2008) didn't exhibit a pronounced dispersion consist in point, such bursts were very remote and as such they were quite energetic - an energy corresponding mass of Sun is released in form of gamma photons in brief moment! In AWT dynamic mass of photons manifests by real mass with gravitational effects, not just a combination of momentum and kinetic energy, as presented by mainstream propaganda. This is because in AWT photon has a nonzero rest mass, albeit quite minute one. Therefore the gamma ray burst propagates through vacuum like dense cluster of photons, tied their own gravity, or like soliton, similar to vortex rings, which can propagate through fluids and gases without dispersion.
The slowing of ligth in boson condensates is based on the fact, EM wave is spreading in form of much heavier electrons, which are revolving around atoms for most of time. Neverthelles the appearance of single photons in vacuum should correspond the appearance of solitons (quantum vortices) in boson condensates.
Because wave packet cannot contain only fraction of wave (it would violate the eigenvalue postulate of quantum mechanics) both wavelength of light, both size of wave packet is compressed in the same way and the shape of vortices in boson condensates is pretty close to appearance of real photons in vacuum - it's just greatly reduced in scale along path of direction.
The cluster of photon ("photoball") is analogous to glueballs, known from weak force scale and it can serve as a prototype of heavier elementary particles. It's formed by dense swarm of photons, where the most energetic and heaviest photons are propagating at the center, while these lightweight ones are revolving center of soliton along substantially longer path, which corresponds the segregation of matter by particle density at the case of massive bodies. This could have testable impact to the distribution of energies along time axis of gamma ray flash: heavy photons should appear at the center of Gaussian curve, representing the gamma burst observation.
Because photons influence mutually at distance in this model, it may be even possible, the lone photon observed in GRB090510 was actually trapped into gamma ray flash during its travel through wast cosmic space, or it could serve as its condensation nuclei in similar way, like particle of dust enables molecules of water to condense into droplet. It would mean, the occurrence of photons of unexpectedly high energy density inside of gamma ray flashes isn't accidental at all and such model leads to another testable predictions concerning gamma ray photons distributions. The "snowball" mechanism of avalanche-like photon trapping has its analogies at the case of rain or snow condensations, laser pumping or rise of Hitler's power before WWW II.
Because photons inside are moving independently to motion of soliton, they're propagating in hidden dimensions effectively: we can say, higher dimensionality of space-time, i.e. symmetry breaking of mass density (inhomogeneity) converts into higher dimensionality of particle motion during sufficiently large space-time interval, i.e. into symmetry breaking of energy density (dispersion). The same mechanism of composite particle formation can be applied onto every other heavier particles or even objects in social systems. All elementary particles are propagating through space like solitons, composed of smaller bosons, which can be illustrated for example by relation of spin projection into axis of motion to speed of particle. The escape of particles through polar jets of black holes can be considered as an exagerrated case of soliton mechanism.
Concerning LS violation, we aren't disputing a lone photons, the exact path of which is unavailable for us - but cluster of photons as a whole, which is indeed quite different situation: at the scope of such cluster individual photons may move randomly along different paths - while they're still keeping the shape of cluster as a whole. Therefore LS remains maintained at the cluster level with respect to dispersion, thus leaving postulates of string or LQG theory intacted - but whole cluster is still moving in subluminal speed with respect to lone microwave photons, so that even lightweight neutrinos can move faster in certain cases. Atemporal logics of formal math, used in these theories cannot handle such situation easily, because of collective motion of many objects at the same moment - although it's still quite trivial to understand. For example, while theories like DSR/DSR2 proposed by Smolin and Maguejio consider violation of LS less or more successfully in 3D, they still cannot explain "violation of LS violation" at both large distance and large energy density scales, which is indeed the case of gamma ray propagation across whole Universe.
String theory could easily model violation of Lorentz symmetry in inhomogeneous 4D space-time simply by declaring it a higher-dimensional flat space in the same way, like LQG - the only problem is, scientists on both sides of ST/LQG duality still didn't realize it, while they're still seeking for signs of both extradimensions, both Lorentz symmetry violation - although they have them before eyes all the time. In addition, here exists an interesting deadlock mechanism: string theorists (ST) could introduce Lorentz symmetry (LS) violation by considering of extradimensions, but they hesitate to propose it, because LS belongs between ST postulates in 4D space-time, while LQG proponents could introduce extradimensions by considering Lorentz symmetry violation, but they grudge against it, because they proposed LQG a just "4D theory" originally.
At the moment, when both sides are earning half of grant support, no one wants to start the reconciliation of both theories by considering of ideas of the dual theory. In such a way both sides are effectively locked inside of ivory towers of their own prejudices. I presume, this example situation explains a lot, how symmetry breaking is occurring at phenomenological level and it illustrates clearly, why theoretical physicists should be payed for reconciliation of existing theories be decreasing of number of postulates, instead of for development of new ones by increasing of number of existing postulates, because divergent character of their formal thinking prohibits them in reconciliation of existing theories.