Doubles Images, But Not Always

Question

Recently, I started using a standalone time base corrector (TBC) called the AVT-8710, between my consumer VCR and Canopus ADVC110, in order to try recapturing certain VHS tapes with problematic sections that previously led to skipped frames in the captures.
(The skipped frames have something to do with the videotapes and/or the Canopus ADVC110, not Final Cut Express or my computer system and peripherals.)
Recapturing the problematic videotapes using the TBC has resulted in captures that playback okay in the Final Cut Express Viewer. The Quicktime files (in the capture scratch folders) also playback okay with Quicktime Player. (The TBC got rid of the skipped frames.) However, when sending the video out from Final Cut Express via Firewire to the Canopus ADVC110 (set to Digital In), and the Canopus analog out to my 720p HDTV, I see lots of double images in the problematic sections where the skipped frames had occurred in the earlier captures.
(This Video Out set up otherwise works okay; the problem is only with the recent captures done with the TBC.)
When doing the same captures into iMovie 6.0.4, with everything else the same, I'll see the double images during playback within its interface, and sending video out only sends audio. The DV files within Package Contents will play okay with Quicktime Player.
What is all this telling me that I don't understand? Obviously, I'm not going to trust that these captures are okay.

Answer 1

It's taken me this long, but I think I've answered my own question, at least partly.
When I explained the captures "playback okay in the Final Cut Express Viewer" and "the Quicktime files (in the capture scratch folders) also playback okay with Quicktime Player" at the top of this thread, I was not aware that Final Cut displays only one field during playback, and Quicktime Player was defaulting to showing only one field during playback. Apparently, that is the reason I was not seeing the interlacing problem (the "double images") during playback of the capture files with those methods of presentation.
I also explained, when sending video out from Final Cut Express to a camcorder or digital-to-analog to an HDTV, I'd see the "double images" during playback. I'm thinking now, when I wrote, "it seems it may have something to do with the interlace video being converted for progressive presentation", I had things reversed in my mind. When outputting to my camcorder or monitoring on the HDTV, then, in fact, I was seeing both fields, which revealed the interlacing artifact.
As for what went wrong during the digitizing process in the first place, I wasn't really expecting to get that question answered on this thread. Nevertheless, comments are welcome.
Reading the "BEST QUALITY QUICKTIME?" thread started by prof d hall on the "Getting started with video production on a Mac" forum was helpful. I tried out the discussed "High Quality" setting, accessible by going into Movie Properties, clicking on video track, then visual settings. And lo and behold, then the "double images" are revealed during playback, apparently because "High Quality" means playing both fields. (I have Quicktime Pro, and assume Quicktime Pro is required to perform this function.)
P.S. I understand, if I save a Quicktime movie file at the "High Quality" setting, it is only changing metadata, not changing the quality. I also understand, if you do this with a raw DV stream file (.dv), Quicktime Player needs to perform "Save as..." and create a new ".mov" file, because raw DV stream does not support the metadata. However, I feel that prof d hall's question about why the file size doubles when going from .dv to .mov was not answered on that thread (now archived). It's easy to see why he may have confused this function with the actual data being saved at a higher quality.