We previously reported on a thermal regime where pure, polycrystalline methane hydrate is preserved metastably in bulk at up to 75 K above its nominal temperature stability limit of 193 K at 1 atm, following rapid release of the sample pore pressure. Large fractions (> 50 vol. %) of methane hydrate can be preserved for 2-3 weeks by this method, reflecting the greatly suppressed rates of dissociation that characterize this ?anomalous preservation? regime between 242 to 271 K. This behavior contrasts that exhibited by methane hydrate at both colder (193?240 K) and warmer (272?290 K) isothermal test conditions, where dissociation rates increase monotonically with increasing temperature. Here, we report on recent experiments that revisit the curious variation of dissociation rates within the anomalous preservation regime, most notably between 255 and 265 K where rates are greater than those at closely bracketing temperatures. Temperature-stepping experiments corroborate the relative rates measured previously in isothermal preservation tests, and also reveal the remarkably reproducible temperature sensitivity of the preservation effect in this thermal regime. These results, coupled with SEM imaging of quenched sample material from anomalous preservation tests, strongly support our earlier arguments that ice ?shielding? effects provided by partial dissociation along hydrate grain surfaces are not the primary mechanism for anomalous preservation. Furthermore, sII methane-ethane hydrate was found to exhibit no comparable preservation effect when rapidly depressurized at 268 K, even though it is thermodynamically stable to higher temperatures and lower pressures than sI methane hydrate. The underlying physical chemistry mechanisms of anomalous preservation remain elusive, but appear to be based more on textural or morphological changes within the hydrate material itself, rather than on compositional zoning or ice-rind development.