Like ppl said above, it's because of the Lv50 Elite.
So because of Runewaker reasons, every flame you cast in that 30 second cooldown will actually try to buff you but you're immune to it >.<
If anything it just clutters your combat log. Which reminds me, a little on-topic anyone know of an addon to remove these flame fizzles from Combat Log and other things like Relationship buffs? They clutter the combat log so bad :/
EDIT: Actually I just saw that it only does it while you have the 10 second speed casting buff. The other 20 seconds are free of that spam.