QuoteShutter Button (50D)
Leave unchanged: obvious
Block during REC: blocks the shutter and related (AF, *) buttons while recording. In 50D, taking pictures while recording would result in ERR99; with this option, you can avoid taking pictures while recording by mistake. Side effect: this will disable image stabilization during recording.
Hold during REC (IS): ML will keep the shutter button pressed half-way during recording, which will enable image stabilization (IS). Side effect: you need to press the shutter button half way to turn IS off before the camera will let you stop recording.
OK, so I know there is a function for holding the Shutter Button in the ML Movie tab but it doesn't work.. when I enable "Hold during REC" and start to record RAW video with the SET button the IS doesn't turn on, I have to hold the shutter-button myself to activate it.. What am I doing wrong, I don't get it.