Missing Scrollbars

Recently, I lost the scrollbars with this theme. They may show up in the first window when I start up the editor, but get lost at the point where I switch between tabs...

The Scrollbars reappear when I switch to a default theme, and they will stay when I switch the theme back to unity - only to disappear again when I switch tabs.

This is the same for horizontal and vertical srollbars.