This affects both Internet Explorer and Firefox, contrary to other Bug reports

When updating the label box at the bottom of the editor (in any editing mode), after typing in the beginning of a label, a drop down box appears of 'suggested' labels. When you mouse-over a suggested label, the window scrolls such that the label your mouse is over is at the bottom of the window.

If it is a long list of labels, this causes the window to continue scrolling, as when it scrolls the first time, your mouse is now over a new label, so it scrolls again, then mouse is over a new label, etc.