Any news on this?
Still happens in 4.8.3 and with svn. We’ve only been using Source Control (Subversion) for four days and already had at least one case (that we noticed) where one developer accidentally overwrote another one’s changes in a Blueprint they’d both properly checked out and committed (one after other, second starting work after syncing first one’s changes).
As stated above, after closing and reopening editor, everything is fine. Updating revision in an external tool (TortoiseSVN), then opening editor also works. (Updating externally with editor open usually fails because “files are already in use”.)