Then I add some sequences to the cuelist, press the play button and when I set a fade of one second, it sometimes takes multiple seconds for it to finish the sequence. specially with LED fixtures you can see it very good since they don't fade that well.

It seems to me that it's the start and end of the sequence that have an extra delay, but I'm not really sure.
It might be the same problem as in this topic:
viewtopic.php?f=6&t=7774