Summoner DoTs not appearing

Time: various
Frequency: sometimes
World name: Hyperion
Character name: Arc Zantusken
NPC name: n/a
Monster name: The Avatar, occasionally others
Class/Level: 50 Summoner
Party or solo: Party
In-game time: n/a
Area and coordinates: n/a

Something I've noticed since the last patch is that my DoTs will occasionally do nothing. This happens MOST often on T8 and with miasma, but I have noticed it on a couple of occasions in AK and T1 with both Miasma and Bio II. I have more than enough accuracy, and I am not interrupting the cast in any way. the cast will go through and that's it, nothing happens. It seems to have something to do with trying to cast another spell right after the current one finishes.