Cannot remove selected keyword with certain movies

Question

Greetings,
I started with a movie file on disk. The format is Apple Motion JPEG A, 1440 x 1080, Millions. I imported it into iMovie '11 a couple of months ago, so it was iMovie 9.0.0. (I am now using iMovie 9.0.2.) The movie was converted to this format: Apple Intermediate Codec, 1440 x 1080, Millions
OK, I can apply any number of different keywords to selected footage. Strangely, The individual keywords that were applied have a dash instead of a check mark. OK. The problem is that I can't remove any of them individually. When I double-click on the dash, nothing happens. The only way I can remove them is to go into the Inspector tab of the Keywords window and click Remove All. So it's all or nothing.
This also happens with footage I took with the iMac's built-in camera. The format of that is Apple Photo - JPEG, 640 x 480, Millions, 24-bit Integer (Little Endian), Stereo (L R), 44.100 kHz.
When I do this with a clip I downloaded from an Apple tech's website (for another problem), everything works fine. The format of that is AAC, Stereo (L R), 44.100 kHz / H.264, 640 x 265, Millions.
OK, I called Apple support and the tech person told me that .mov files are not supported. Say what? Why should this matter for something like keywords? I can work with individual frames just fine. I can split clips, add music, and so on. Shouldn't that be enough, esp. the ability to add a soundtrack and pin it to a particular frame? He says the .mov files are "finished products" and are not for editing in iMovie. What? He suggested using Handbrake or similar to convert this to another format. David Pogue's iMovie '09 book says that the very purpose of AIC is to facilitate the editing of high-def video (p. 43).
Can anyone explain what in blazes is going on here?
TIA.

Answer 1

Probably you sorted this by now. I had this same problem.  For those who come later, check the Couldn't remove keywords .... discussion.