KDE 3.1: Double-click on menu button in titlebar

I've just gone up to KDE3.1 from 3.0.4. Previously, I could close a window by double-clicking the leftmost button in the titlebar. That doesn't seem to work any more. I've hunted through the configurations, but I can't seem to find a way to turn this behaviour on. Any ideas? Thanks, Matt -- "It's the small gaps between the rain that count, and learning how to live amongst them." -- Jeff Noon