I had a problem once when my heel wasn't going all the way into the binding until I took a few heelside turns-- then my toe straps were loose. The binding was just a bad fit for my boot.
Hmm, that could be it but everything seems to fit nicely when I first strap in; my feet only start wiggling around towards the bottom of the run.
Also, I have one last (really) question. As you can see from the picture of my bindings that I posted earlier in the thread, the end of the straps sit in a channel. How do I remove the straps from their channels? There are no screws or holes or anything on the outside of the channels. I don't think my bindings are that strange; the majority of the other pictures of bindings I've looked at have this same channel.
Here's the same picture from earlier with the channels (except the back right one which isn't visible) circled: