iMovie Captures Faster than Normal Time

I just bought a new dual core 27" iMac. Last night I tried my first capture from my HV20 with iMovie. Everything seemed to work out great. I had it set to full (highest quality or whatever that option is) and 16x9 and it started capturing perfectly. When I returned to my computer though and reviewed the captured clips, about the first 10 seconds of the 20-30 minutues was in real time but the rest of the video was like one and a half times faster (or so) than real time. To my knowledge no settings were changed on my camera during the filming process between the various shots.

Any thoughts as to why it would capture at two different speeds and how to fix it? Thank you all.