Error on Calendar View

Hi, I have a weird error popping up for some users in their calendar. When they add Saturday and Sunday to days displayed in a work week, and then select the one work week view, all their appointments and meetings get pushed up an hour. It will still be 1:00 to 2:00, but will show up in the 2:00 to 3:00 time slot. Has anybody run across this?

Thanks

Sean