A similar thing happened to me this past weekend. The girl and I had brunch and the place was cash only (I had to go get some at an ATM) -- so instead of unlocking my bike which was locked to the actual rack (hers was locked to mine), I got on her bike which is a 48cm (I ride a 53) SS (which I built) and headed off. Boy, did that throw me off!

I started to ride and since her seat is way lower than mine, I had to do a bit of that BMX style riding. Thus, it surprised me when I wanted to bring the pedal back up, expecting the rotation to help me a bit but then it didn't. When I brought it to speed, the bike worked fine.

I'm not sure if that was a dead spot (could be and it was a lazy sunday so I wanted to just cruise) or if because the saddle was so low that I couldn't quite get the proper rotation through the cycle.