Note: incredibly minor bug report, just something I noticed earlier today.
When moving one's mouse cursor over any part of the menu bar (the "File", "View", "Favourites", etc. bar) -- including the empty areas -- for some reason the miniature minimise/maximise/X buttons flicker occasionally. It's almost like RedrawWindow() (against the MENUBAR HWND rect) is being called unnecessarily on some WM_COMMAND messages (or maybe WM_DRAWITEM?) relating to mouse cursor positioning.
I don't have any other GDI applications handy that have the miniature minimise/maximise/X buttons mIRC has. Are these using MIIM_BITMAP or are they something custom?
Issue is 100% reproducible on Windows 10 Pro 22H2 19045.4651, but not immediately noticeable until you really sit there moving your mouse in the menu bar area.
Issue could also be a Windows bug/quirk, in which case nothing to do/fix
Thanks Khaled!