Please note that Win7 was released after mIRC 6.35, thus there, probably, are a few issues which Khaled will have to handle one way or another before the next release.
In my experience, Khaled does a great job of making mIRC handle the changes that a new OS version requires, while maintaining compatibility with previous versions of the OS and/or previous versions of mIRC.
Thus said, I haven't encountered this situation with Win7, but then again I'm not using the same version of Win7 that you have stated.