I have 2 video tracks on top of each other, I'm controlling the opacity of the top track with keyframes. only the 1st keyframe is registering any effect: when I have it set to 100% the entire track is visible, 0% and the entire track is invisible.
I have only 2 active video tracks, both time remapped (1000% and 50%). (although even when I delete the track below it still fails to work). I'm using 5.0.3
Do your time remapping, nest the clip into a new sequence, and then add your opacity keyframes to the nest. This forces opacity to be applied after the time remap; otherwise, the opacity is applied before the remap.