so from my understanding in the tooltip the next cast is supposed to be an instant. however after i use Swiftcast and then use something like Medica or Raise or anything that needs to be channeled. it still brings up the cast bar. the spell does not actually go instantly. the cast bar just goes very very quick. like a blink of an eye quick.

i have had several times wasted a Swiftcast use, because the spell is interrupted. what is going on here? why is Swiftcast not truly instant? why can a spell still be interrupted?