For me, im not sure if it was optifine, but I also tried with a vanilla client; Whenever im playing, people will always be in the wrong spot they should be in. Like someone would be swimming, but instead of stopping at land they would just keep on swimming thru the land until. it looked like the got out of the water, in the land. So basically whats happening is that The players are still moving normally, just their actual location is off, and there's no way I can hit them when that happens. Are other people getting this or is it just me?
EDIT: I'm guessing because lots of other people are complaining about something I think is what i described, its probably server-side. Unfortunatly, this has also rendered MCSG unplayable until its fixed for a good majority of people, so maybe change about half of the servers back to 1.4.2 until this is fixed?