Mage FireIII, Blizzard III reduced cast speed with lvl 40 trait not working 100%

With lvl 40 the Thaumaturge receives the "Magick and Ment II" Trait which allows stacking Astral fire and Umbral ice up to III. Level III AF or UI (Astral Fire, Umbral Ice) grants the new buff effect : "Spells of the opposite element have reduced casting speed".

so basically we can "spam" Fire III and Blizzard III with like 50% reduced castspeed which is nice, but it doesnt work flawlessly.

First: sometimes Fire III or Blizzard III doesnt remove the current stack of AF/UI or refreshes it. it just does nothing even tho it was casted.

Second: when i cast Fire III and instantly start pressing the key for Blizzard III (even with global cooldown restriction) it somehow lets me start casting Blizzard III instantly after Fire III but without the castspeed buff.
This leads to normal casttime and often "bugs" the cast animation, meaning : even tho the cast is finished, the char still stands there casting, castbar already finished long ago.

This is basically everything ive encountered so far, if some1 else has similar troubles or already a solution then please let me know.