I have a Sony DSR-250. I am sure that the white balance was on manual. I was able to recreate the issue and it was related to shutter speed because the issue goes away after the shutter speed is put on manual.
I have experienced the same problem many times. I seems when FCP is trying to appropriate HD space for the video it is about to digitize, it gets suck. Then you end up with the huge file you mentioned. This has happened to me on two different machines. If I find anything else out I will post it.