Part Losing Transparancy in Simulate

I have a part in an assembly that is set to transparent. As soon as I switch over to a simulation study tab (at the bottom of the screen), the part loses it's transparency. I have to find the part in the model tree & make it transparent again. Any time I switch out of & back to the simulation study tab, the cycle repeats itself. I have never seen this happen before -- any thoughts as to why this is occuring?