In the early alphas and betas of VersionPress, we encountered an issue with "date modified" -- specifically the DB columns post_modified and post_modified_gmt -- which was causing issues in revert scenarios (and would later cause issues during sync). We then decided to compute the date from the Git history, see #73.

However, that was a bad idea. We missed one important scenario: posts that were created before VersionPress started tracking the site. We currently do not have any information about them in the Git repository so restoring them by wp vp restore-site command or in sync scenarios gives them wrong post modification dates.