Scrolling on tabbar can cause apps below Vim to receive scrollwheel events

Binary package hint: vim

Ubuntu 9.04
vim package version: 2:7.2.079-1ubuntu5
(my apologies if it has since been fixed)

To reproduce
1. Run `vim -g`
2. Disable menubar
3. Enable gui tabs
4. Open a new tab so that two or more tabs are open
5. Place cursor between tab text and textarea border (it's only a pixel or two tall, so it may take some hunting)
6. Scroll the mouse scrollwheel
7. Observe app (desktop in my case) react to scrollwheel (change workspace in my case)

Intended behvaior:
Change current tab or scroll the textarea.