First off, you don't really have the right to request that a "discussion be locked" just because you're too childish to back up your arguments. It seems like you're interested in making sure you get the last word, regardless if you're right or wrong. Grow up.
Why doesn't mIRC be sure that scrolling messages -do not- make it to the MDI base when the client is maximized?
Because the user might WANT those messages to make it to the MDI base. Their reasoning might be invalid in your opinion, but there is no reason to deny a user functionality because your driver is broken. Instead, tell your manufacturer to fix the driver. Simple as that.