Individual solar cells running warmer than the rest of the panel

verdigo

I was sweeping snow off my array after a pretty big snow a week ago. It was cold and the snow was the light drier kind, so it was coming off no problem except on a few individual cells where there was a layer of ice in the rectangular shape of the cells.

The only way I can see this happening was if those cells where warmer at some point than the others on the same panel. It doesn't seem to be affecting string output. However it worries me that there may be an issue with a diode letting current flow into the cell when it is not suppose to or a problem with the cell's internal resistance. 

I have thus far not educated myself on the internal workings of a solar cell so my assumptions may be way off.
Comments?

Dennis