MultiText Scrollbar Displays Oddly

In a hard-to-reproduce situation where the amount of text is just big enough to make a multitext control have a scrollbar, I've noticed that the scrollbar doesn't behave properly. Instead of sliding down and stopping, the tab keeps sliding below the range in which it should move, and the text keeps scrolling up. You can eventually scroll the tab right off the visible height of the bar using the mousewheel. Attempting to drag the tab with the mouse keeps it where it should be: centred in the bar.

This was observed when viewing a tech description, but the exact tech in question isn't likely to reproduce this unless you're using the same resolution and font size.