Well, this one was hard. It took me 5 hour to figure out what is going on and another 10 hours to fix it.
The basic problem is that MT in Win32 is really stupid and we have to do a lot of uninntuitive workaround to get it working. And in these workarounds, we had bugs...
Anyway, all should be fine now. Please check.
Given the complexity of the issue, I expect to fix more bugs there in the future. But for now, reported issue is solved.