It seems that the new file menu that's hidden unless you press alt isn't working correctly.
It seems to work on KEYUP, and an alt-tab away from the app makes the menu show up then dissapear, when I'd guess that it shouldn't show the menu at all.
A simple check to see if mIRC is the active app when alt is UP, should fix it.
Sorry if this is intended behaviour (which I imagine it's not)
I should note that i'm using WINE and mIRC v7.02 (beta22).
To reproduce: Have mIRC maximized and another window shown but not maximized, alt tab away from mIRC.
It may not happen on Windows, as above I'm using WINE