My sentiments exactly. I have used Parallels for 4 years to do daily software development work using a MBP and two external displays, and now I cannot use PD12 because of this issue. I used to recommend Parallels to my colleagues as a great solution, and now I no longer can.
As a software developer (and, ironically, former high-profile PC/console gaming developer), I can appreciate the challenges in supporting fullscreen well -- in fact, when I used to work on PC games, fullscreen support was the bane of my existence. However, we had no excuse and had to make it work because our customers demanded it.
I'm tired of checking these forums every day trying to see if there's a fix for this problem, and being stuck using the older PD11 even though I've already paid for my license renewal. I'm ok with waiting for a proper fix; these things take time to do right -- I just need to know someone's actually trying to fix it.
What I would really appreciate is someone from Parallels (Dmitry, perhaps?) at least telling us whether they are attempting to address this issue at all.
Thanks for listening.