1920x1080 Exporting as 1888x1062

I'm using iShowU HD to perform screen capture for a demo video that I'm making. The screen area to capture is set to 1920x1080 and everything to be captured is within that area. When my capture is finished, the resulting QuickTime file shows everything, as does the Final Cut sequence. When I send it to Compressor, it also displays the entire capture area.

However, when the conversion in Compressor completes, some cropping has occurred. The video is now 1888x1062. Since it is a web video, I had things on the edge of the frame, but not completely off the frame. These things are no longer on screen.

I'm confused as to why this is happening, since my Final Cut sequence was HDTV 1080i (16:9), Square Pixel Aspect Ratio and Apple ProRes 422 compression, non-anamorphic.

It's worth noting that if I export straight from the Final Cut sequence (Export to QuickTime Movie), the same cropping results. However, if I export using QuickTime Conversion, it exports as 1920x1080, so long as the export size is 1920x1080 HD. If the size is set to HD 1920x1080 16:9, then cropping results.

I'm fine exporting via QuickTime Conversion, but I had hoped to use Compressor so that Final Cut isn't tied up...

In Compressor, I was using the QuickTime H.264 setting. Frame width & height all at 100% of source, 1920x 1080

Using Final Cut 7.0.3, Compressor 3.5.3