Ok, I'm trying to change the duration of a fadein/fade out dissolve transition to less than one second, but it doesn't work. Whenever I try to change it from 00:00:01;00 to 00:00:00;50, it changes it to 00:00:01;20! Why is this?

EDIT: By the way, this is in FCP 5.0.3.

Sorry if I'm not understanding your timecode example, but in NTSC the frame number (;50 in your example) has a maximum value of 30 which corresponds to 30 frames per second. So perhaps that is your problem?

I believe it is not set to fps but rather actual time such as 00:00:01;00 = h:m:s;ms

Ah, OK... sorry I never use that format. I would still imagine that you're limited to increments of one frame (1/30 sec) - whatever that works out to in your format.