Yikes – this bug is a doozy. I have spent hours trying to figure out what’s going on, to no avail. My last attempt to fix it involved deleting working copy and checking it out using exact same SVN binary that ships with UE4. (I heard UE4 is “picky” about what version of SVN is used to check out a project.) Unfortunately, this did not solve problem.)
It’s really a shame, because this makes Mac version of UE4 a tough sell for projects versioned by SVN. In my experience, relying on external version control for UE4 is super dangerous unless you’re very, very careful about what files you commit or don’t commit. Accidentally committing wrong files can lead to corruption and general weirdness.