This may not be a bug, but it is an observation. Sometimes the playback (not replay playback -- just normal play of action after the Warm-up or Match button is clicked) of online matches will show oddities such as skipped frames during player movement or choppiness of movement; also, sometimes movement will slow and then return to normal during a point or say during a serve (like the clap from a player after a good point will be in slow motion). For example, in one match, during normal play, I see the my player slowing during a rally, as if time is slowing for him (looks like he is struggling to move); but if I press F1 and watch the replay at normal speed, the slowing isn't visible. In this case, in the actual online match, there was slowing of movement for my player during this rally; so, what is seen during the normal play of the recording is correct, but the replay of the action (F1) seems to take out these inconsistencies (so there is a difference between what actually happened as seen with normal play of recording and what the replay shows).
Maybe this information will help ManuTOO in some way. I can post a recording if it would help.
Thanks.