Noticed one weird thing when i was using this simple macro on my buffers:
/useskill buff1
/useskill buff2
...
/useskill buff12
When character has 956 cast speed or higher, skills are being used without delay and macro casts 12 buffs in ~13-14 seconds.
When character has 919 cast speed or lower, next skill casts only when the previous one is off cooldown which leads to delay between casts and macro finishes in ~22-23 seconds.
956 and 919 are the closest numbers i could get using available combinations of sets and buffs, so i don't know exactly at what point bug(?) appears.
I tried commands like /useskillforce or /delay 0, didnt help. There is no delay when i cast manually.
Tested this on 3 different characters, tried casting without spiritshots and got the same results.