Are the files with modified timestamps still ok? (no changes to the contents or checksum?)
Do you see any pattern to this? For example, do all the modified files have very long file names, or unusual characters not used anywhere else?
Does this affect all the files in a particular folder, or is it more random?
I did a bunch of testing during beta. My experience was file dates were preserved, however folders containing a subfolder lost their time (on the folder - never on the files). 1.5.0beta2 - Large Vault Migraton Feedback