there are a lot of graphical problem in solidworks. they cant fix this issue, dont wait for solve.
A call to my VAR finally illuminated this problem.
Apparently SW added a function to the Section View dialog:
If "Show section cap" is NOT checked, all section planes appear as transparent and thus, hollow, making them look like surfaces, not solids.
I'm sure there was a reason for providing this new feature. I could not find out if it is checked by default or not.