The shutter speed won't update on 50D's Live view screen. The shutter speed can be changed without issue, however, just the number on screen would not exceed 1/30th of a second. Not sure if that's a bug or an enhancement.
Can you check if shutter speed displayed by ML is correct?
It should match Canon display... sort of. I believe 50D is NTSC only (30fps), so it might only show 1/60.000 (other values may be not be exact).
In PAL, you should get 1/33.333 and 1/50.000. But since 50D doesn't have any PAL video modes, you may not get these values. I don't know.