and I noticed it always produces a slight delay before each AB. Using AB on its own does not have it.
I also confirmed it on another spec and another spell.
It appears to be around 200ms. Much lower than the GCD but very noticeable. The number is a guess.
PS. The example sequence has no real use but I first noticed it on a sequence that included Mirror Image. At first I suspected an issue with MI, but removing it did not alter the latency effect.
EDIT: I suspect it has a simple explanation: The cast buffer may not be taken into account at all hence, to produce latency equivalent to world latency.
Could you post this in our bug report sticky please? This will help us keep track of it:
4.2 Known Issues & Bug Reports