I hold control and scroll with the mouse wheel to change the size of the text in the scripts editor. The numbers on the left which represent the line numbers don't change in size so the alignment goes all weird. Dunno if the scrolling part is a bug or the not changing size is a bug :P
Ctrl+scrollwheel is a general richedit shortcut, so its not a bug. This is most likely happening because that event is not being caught by mIRC and the line numbers font is not being changed accordingly.
This appears to be a richedit feature - unfortunately the only safe way to resize the fonts in the script editor is through the Font option in the File menu. I'll see if I can make mIRC handle this key/mouse combination for the next version.