They're calling build 3120 a Release Candidate, and putting a lot of work into coexistence with Boot Camp; while apparently ignoring a serious regression in full screen video. In full screen mode, a program that attempts to change the screen resolution will fail to do so regardless of Parallel's video preferences. The last version in which this worked correctly was beta 3036 (and of course the released 1970).

So if you run full-screen Windows apps that need to change the video resolution, stay away from 3120.