if a problem is not reported then no needs to wait a fix for an unknown issue.
Where are the reported bugs ?
Have you installed the wine debug package ? then ran your game with winedebug into a terminal ?
I successfully downgraded to 1.5.19, but I just wanted to comment that this doesn't actually solve the problem with 1.5.20. Now that I know that a bug report has been made, I look forward to seeing this problem being fixed.
I've been using the latest wine releases for a few years and this has been the first time I've ran into a serious problem, which required a downgrade.
A new ppa release, 1.5.20-0ubuntu2, fixes the problem. Seems to have been either a faulty patch or build.
Currently running Ubuntu 12.10 Quantal Quetzal (64bit) installed on core i7 950/ 6GB/Geforce GTX 460 SOC 1GB system.