Jerky Video Exported with Premiere

Question

I'm having some trouble with Premiere Pro CS5, in which the  files it creates come out jerky / choppy. The problem isn't the source, as the  last time I encoded the same video it came out fine, and the problem  isn't the encode settings, because they match the previous encode I did.  Rather, something is happening to make the video I export appear  slower, as though it were rendered at 15fps instead of 23.97fps.
I'm exporting as H.264, .MP4 container, 15MBit CBR, and 23.976 fps,  which is the same as the previous video I did, which used the same  source. Is there any setting that could have changed in Premiere that  would cause everything I export to appear really slow? Furthermore, is it possible that there's some setting new to CS5 that's causing this problem, as my work in CS4 came out fine.
The footage came from an AVCHD camera, and the files are .MTS. Playing back an MTS file doesn't have the issue, but if I play anything Premiere has encoded, the problem is evident, regardless of export framerate or other settings.
Any ideas?

Answer 1

I'm playing the video back on the same computer used to encode it. The problem is definitely not the computer, as other encodes I've done can be played back fine, and I've also tried different computers. The audio doesn't stutter at all, and the video never loses sync. Rather, all the action is just really jerky.
My source material is indeed 23.976fps wrapped in a 60i container.
No idea what field reversal is. Nothing Matrox in my system.
More details about the video itself; the video is a two act play. Act two was encoded with CS4 using the same settings, and came out just fine, with very fluid motion. Act one was also encoded with CS4, and this came out fine, but for other reasons I can't use this copy (screwed up the bitrate, but the copy visually looks fine), and the computer running CS4 no longer has it. The camera never stopped rolling during the two-act play, so the video parts should be indistinguishable for a computer.