Using 500D, with February 4th autoexec:
If you enter the ML menu while recording a video, the FPS override option becomes disabled until you exit the menu. You can see through the transparent menu how the video changes to darker (and smoother), or at least when you play back the recorded video. The effect is of course more pronounced the smaller value you use for the FPS override. This bug prevents you from changing various settings on the fly, if you want the video to look consistent.
I noticed this problem while recording a video which required white balance and exposure adjustments every now and then.
Also, every time you toggle the magic zoom box on or off (when using fps override), there's a similar effect but it only lasts for a split second. I don't know if there are any more ML related functions triggering the effect.
If you need any additional information, let me know.