Now that I think about it, that happens to me when I sit on a hard chair also!
...I think that might have to do with the fact that I am so short that when I sit in most standard chairs my feet dangle, not touching the ground. I'm pretty sure that puts pressure on the back of my legs, kind of my hamstrings, and makes my legs/feet go numb. Maybe there's some sort of link between that and my toes-numb-while-riding thing.
I did move my cleat back and that seemed to help some. But maybe I will just have to resign myself to getting off and walking around every so often.

Thanks for the advice!