Top frame missing

I've just noticed that my footage (DV PAL, FCP 5.0.4. and Mac OS X 10.4.11, QuickTime 7.1.2) looks different in the Viewer than in Canvas. Yes, it can be seen on the monitor as well.
It looks like a top frame is missing, and it goes across all my footage, all hard drives, all projects, few years back.
Somehow, I can't believe it was there all the time, and that I haven't noticed it.
All footage is shot with two Canon XM2.

As you can see it on the image attached, it becomes obvious when footage is resized.
I don't ever use this sort of picture in picture, so that is not the issue,
I always use a split screen with a frame or two of black background in between.

What worries me is that top frame is missing when watching clips in QuickTime as well,
same happens on other computer, so it's not FCP I believe.
When stills exported from both Viewer and Timeline, they both look fine, no frame missing.
Both stills showing 720 x 576 pixels in Photoshop.


Finally, I've got a little Sony camcorder, for ingesting and rewinding tapes and for filming occasional family
stuff when bigger camera is inappropriate.
Footage from that camera is OK, "all frames" are there. Both when resized in FCP and when watching it
in QuickTime, you can clearly see the footage goes to the top of the window, no black line.

So, it looks like it's Canon.
Still, why it looks OK in Canvas / Timeline?
And second question, is there a way / setting to get rid of it? I know I can crop it, but am I missing something here
(apart from a top frame:) ?

Mio