I have played a little with configuration - Chipset Extra was set to generic, sound disabled, network (bsdsocket and uaenet) disabled, but it didn't help. Disabling RTG is not an option on a system with AfA, PNG icons only, and all this true-color goodies
I am going to take some time to find a minimal WinUAE/guest OS configuration that causes a problem - but this will take a little time.