Thanks for the info, guys! I did not realize it was cropped. This is why VLC playback of the .mkv shows no apparent differences. :)
I have no objection to just getting the AVCHD version (unless it is missing audio tracks or has reduced bitrate). I already spent the time getting the .mkv, though, so that is what I am working with. Again, it worked fine in the past and now I know why.
UncropMKV sounds intriguing. I will take a look at that.