Ed,
The common installation directory is intentional so as to share resources – makes more sense when you are installing using Pulse as opposed to an offline installer (due to common plugins which haven’t changed, you need to download much less).
Of course, here it seems to have had the reverse effect and is obviously unacceptable. We were unable to reproduce this when we tried, but my team is looking very seriously at this problem.
Sincerely apologize for the inconvenience caused, thank you for reporting the issue.