I can also confirm this bug. It's noticeable locally as well, not just over RDP -- you just have to have good eyes. I see this behaviour in both Windows XP SP3 as well as Windows 7 Ultimate x64.
And I can confirm that mIRC 7.23 and earlier does not have this problem, but the issue began with 7.24 (beta).
I'm under the impression there is some broken code that is calling a window refresh for no justified reason that I can think of.
versions.txt doesn't mention anything about the window redrawing code/bits being changed, and the only things I can find which look even remotely relevant are:
4.Fixed hotlink feature not handling certain characters for addresses and channels.
11.Fixed DCC window bug that resulted in text not being displayed correctly when toggling MDI/desktop mode.
18.Fixed track urls bug that prevented it from working if the URL catcher feature was turned off.
20.Fixed custom window not remembering font setting when MDI/desktop state of the window is changed.
Khaled would need to chime in here with details of what changed.
