If my trackpad is sending the messages to the wrong window, and mIRC is failing to handle those messages correctly, then it would still appear that it's not a driver bug. This is because it only affects mIRC, and not other MDI software.
I request that this thread be locked and preserved as evidence of this scenario's occurence, as I'll be blogging about it today. I've said all I need to say to establish my point. You guys seem to be jumping to the conclusion that it's a "driver bug" and that drivers should not be sending scroll messages to windows that don't support them. In that case, vertical scrolling should only be allowed when the mouse is above the buffer textbox, and the fact that this isn't the case is also "a driver bug".