Im using Windows 7 beta (it also happened in Vista) and regularly mirc loses its aero border switching back to basic (other applications are unaffected).
This can often occur simply by switching to another application.
This has been reported, it happens when there is unicode in the topic and the channel window is maximized because mIRC tries to custom draw the titlebar.
- argv[0] on EFnet #mIRC - "Life is a pointer to an integer without a cast"