that whenever an actor was saying their line, Mark-Paul would always mouth the same line, and then say his line? I just noticed while watching the first DVD, and he did it quite often.

No I have nervery noticed that

i am going to look at that

He seemed to do it more in the early episodes. I noticed a lot of it in season 1, and some of it by season 2. He cut it out by season 3, though.

yea i cant recall him doing that in the later seasons

This happenens to alot of actors, especially younger ones in first seasons of their respective shows/sitcoms. They're becoming familiar, too familiar with the script, so much that it leads to them mouthing other character's lines. For Example, In The Fresh Prince of Bel-Air, Will Smith is seen several times throughout the first season mouthing other character's scripts as well.

oh yea they mentioned that once