The issues you raised are extremely minor Win7 issues, one of which was a dup (which you knowingly posted anyway; I suppose because you only found 2 real issues).
They occur relatively rarely and have very simple workarounds (one of which is "don't put your mouse on the switchbar or move it 2 pixels over if it is"). They might be minor annoyances, but I can't see how you draw the conclusion that mIRC is less than fine on Windows7. Every version of mIRC is going to have minor bugs like these; mIRC is still completely usable, and in your case, moreso than 7.x
