If your opponent saw you miss the ball or put it out, there's no reason for him to give you the point...
92% of online matches are totally desync free ; on the 8% with desync, I guess there are about half that comes from people trying to play online with Mods. 1% is probably from network issues. So that gives about 3% from engine troubles. I'm always trying to figure out from where (coz I'd really like to have the .Dmo 100% desync free, that'd be quite helpful when debugging stuff), but keeping sync in Peer Network is 1 of the hardest tasks in video game...
I just found something that may have been leading to desync, and it'll be fixed in v1.0d, so hopefully the number of desync will lower a bit.