moving the mouse in the bottom 2/3 does nothing. not sure if this is a bug or intended behavior.
To me, it appears as though mirc is allowing the bottom 2/3's so if you wanted to select a long line of text wiht the mouse, you are able to without opening the nicklist while doing so. I would like to ad tho that the nicklist show/hide (imo) should use a "smooth" scroll, not there it is--there it isn't. Maybe even the option to have it smooth scroll to save those with les cpu power. I just think that the show/unshow in that "raw" form is unpleasing to the eye, where as a scroll would be a little more --well, not soothing but just more pleasing.