On the occasion of a DSM 5 beta evaluation I tested the opacity option for layers again - and found it is (still) not working.
Changing colors works fine, also the mouse-hover effect with DSM 5.
As Tim Heeney reports here that it works for him, the cause is likely some DSM, graphics driver or operation system setting.
I have Windows 7 SP-1 64-bit running, and I tried various 'Graphics performance options' including 'Custom' that DSM 5 offers - without effect.
Any hints?