After some testing, I've found that many control wizard spells that have to be pressed more than once to cast does not benefit from the Thaumaturge feat Spell Mastery. This includes Shard of the Endless Avalanche, Ray of Enfeeblement in the Tab slot, and Icy Rays but oddly enough, in the case of Icy Rays, it ONLY occurs when it is in the Tab slot.
These spells do not have their cooldowns reduced by Spell Twisting.
Notes: Have not tested Imprisonment, which can be canceled early, on account of not having it skilled.