Can you post a log file please? I haven't noticed that happening. That's really more of a PvP setting though (or that was my aim behind it anyway, not saying it cant be used in PvE effectively).
Log is to big, I will make another this evening...
but here is a short passage:
22:06:14.856 D] [CGSpellBook::CastSpell] Override ID: 686, KnownIndex: 71
[22:06:14.857 N] [Demonic] [Casting: Incinerate] [On: Frostspeer der Zandalari]
[22:06:15.438 N] [Demonic]
Canceling Cast - Found a unit to Shadowburn!
[22:06:15.600 D] [CGSpellBook::CastSpell] Override ID: 172, KnownIndex: 48
[22:06:15.601 N] [Demonic] [Casting: Immolate] [On: Frostspeer der Zandalari]
[22:06:16.093 N] [Demonic]
Canceling Cast - Found a unit to Shadowburn!
[22:06:16.277 D] [CGSpellBook::CastSpell] Override ID: 116858, KnownIndex: 38
[22:06:16.278 N] [Demonic] [Casting: Chaos Bolt] [On: Frostspeer der Zandalari]
[22:06:17.303 N] [Demonic]
Canceling Cast - Found a unit to Shadowburn!
[22:06:17.333 D] [CGSpellBook::CastSpell] Override ID: 116858, KnownIndex: 38
[22:06:17.334 N] [Demonic] [Casting: Chaos Bolt] [On: Frostspeer der Zandalari]
[22:06:18.345 N] [Demonic]
Canceling Cast - Found a unit to Shadowburn!
[22:06:18.354 D] [CGSpellBook::CastSpell] Override ID: 172, KnownIndex: 48
[22:06:18.355 N] [Demonic] [Casting: Immolate] [On: Frostspeer der Zandalari]
[22:06:19.850 D] [CGSpellBook::CastSpell] Override ID: 116858, KnownIndex: 38
[22:06:19.851 N] [Demonic] [Casting: Chaos Bolt] [On: Frostspeer der Zandalari]
I would take a look in to the code myself, but since it's binary-code... :-/