For instance, on some pieces the violins have a tendancy to speed up (then usually complain that it was too fast). Also some people don't have any idea of dynamics (ie volume). Then, there are the ones who can never seem to remember how each piece is played - we often change some of the music so its not as long, drop a repeat here etc. Nothing much, but it makes it shorter and easier on us and any audience. How many times do we have to repeat the same instructions (several times) every week.
Hey ho, thats life. At times playing feels like a big fight - playing solo is different to playing in a group. I wish some people would remember that.