I've got a problem with the latest ML firmware on my 550d: If I start recording a movie shortly after turning on the camera the buffer overflows after a few seconds and the recording stops automatically. Sometimes this happens even if I give it a second, a third or a fourth try. Sometimes the recording even stops automatically although the camera has been turned on for several minutes! I have this problem with both a 32GB Silicon Power Class 10 SDHC and a 16GB Transcend Class 10 SDHC Card. In the ML settings, I deactivated everything except for audio monitoring and cropmarks (I deactivated AGC too, of course :)). The strange thing is that this problem disappears with deactivating ML on the camera's startup. So the SDHCs can't be the problem. I also had not this problem with earlier versions of ML.