I have a coarse pepper grinder, and it says not to grind over steaming pots, why is that? It says not to grind over steaming pots on the label of the pepper grinder. Is this so you don't get burned or for some other reason?
There are two possibilities I can see:


The steam can wet the pepper in the mill and cause it to cake in the grinding mechanism
There's an over-protective lawyer worried someone will scald themselves and blame the grinder company. 


Which of the two is your guess. Personally I use my grinder over steaming pots all the time and I've never had any problems, but YMMV.