Glad I'm not the only one who find this annoying.
As mentioned already most windows apps behave this way, (menu bar is activated even if not hidden).
mIRC is the type of application where you sit around waiting, either for a reply, or similar situations, doing so I tend to get fidgety and sometimes hit alt. In other situations it's hit by accident. Whenever I do the menu bar (which I never use) pops up, making the window bounce around and such. Half of the time hitting escape does not close it again so you have to alt tab or grab the mouse to get it to go away.
I'm not saying this is a huge problem, but whenever it happens I think about reverting to 6.35 and get annoyed. I doubt it would be a huge issue to make it a option.
I don't see how a extra checkbox would be a problem, but if it is, make it accessible only trough the mIRC.ini file. *shrug*
