Sorry you're having that problem. I'm not sure what the solution is, but I did want to suggest that you edit the title of your question (I assume Bookdown contest submission: wasn't what you intended) to be sure that the IDE devs see it.
Thanks for the bug report! We're aware of the issue and plan to release a new preview release later today to rectify the issue. Sorry for the trouble and thanks for taking the time to test!
Installed 1064. Problem with git window ok, but after some work my computer froze: I realized that about 30 copies of RStudio were running! Never have seen this before.
Yikes! That's certainly not expected. We try to keep the preview releases as stable as possible; sorry to hear something like this has snuck in.
We plan to publish a new preview release soon; if you're still willing to give it a test drive we hope you'll find it behaves better than the current iteration of the release has.