Visual bugs in the Tree tab of the "Document index" on IE8 and IE9

Steps to reproduce:

• Hover over "Wiki" and click on "Document Index"
• Click on "Tree" and expand some of the spaces

On IE8 there are only "-" signs to the left of any space/page whether it's expanded or not and also there's no scrollbar. On IE9 there are "+" and "-" signs, but also there's no scrollbar. I've attached screenshots.