During the Directory Migration and Synchronization, if you merge migrated user accounts with existing target user accounts and later undo the action, the original passwords of target accounts are not restored. Restoration of all other attributes is not affected.
Migration Manager is unable to determine which password hash was originally set before the merge. So when a undo is performed, the current password is left.
Please note that this does not effect any other attributes, only passwords.
There is no resolution or workaround to this issue at this time.