No finger touch circles in iPhone simulator

I'm developing an app on the iPad, and trying to detect multi-touch events. The events are working fine, but in the simulator, I'm not getting the little circles that开发者_C百科 show you where you're touching. Not so much an issue for single touch, but for multi touch, it's a big pain. Any idea why these circles aren't showing? I think it's something with my machine (MacBook Pro), because on another MacBook Pro, the circles do show up.

Edit

I've discovered that this problem only happens if the scale is set to 100%; if I set the scale to 50%, the circles show up.