Okay brief overview:
1) Chogall summons fire elemntal and then absorbs it
2) if the add has 100% health when he absorbs it, he gets 10 stacks of Flaming Destruction
3) if the add has 0% health when he absorbs it, he gets 1 stack of Flaming Destruction
4) So when the boss melees you (including blocks) you take fire damage.
So something here is likely a bug, but i thought i'd post it for the sake of completion.
This combat log is a little deceving. When I call for an add to be absorbed as a 10 stack, I'm on a 400 resistance trinket, shield block, shield wall and mashing spell reflect. (@685 total resistance). With a 0 stack on an add I can do it with only shield block. The benefit of not dpsing the add, is that you can put another 735k damage on the boss instead.
The cooldowns are there just in case he sneaks an attack through in the 1 second of downtime on spell reflection. (turns into a ~65k hit with ~80k resisted). Glyphed for 6 second CD, 5 second uptime.
Here's the kicker: The spell doesn't actually get reflected, which is why it doesn't consume the spell reflection charge. Read as: Spell Reflection doesn't fall off after it "Deflects" a Flaming Destruction attack.
http://i51.tinypic.com/15heno5.png
So first add is a 10 stack with shield wall, shield block, 400 resist and mashing spell reflect.
2nd add is a 0 stack with shield block and mashing spell reflect.
This is kind of interesting:
If you intervene the other tank when cho'gall has flaming destruction, you can spell reflect the fire still. Meaning if you glyphed intervene you could pull out two melees and two fireballs (which then deal 0 damage).
http://i52.tinypic.com/hv0yok.png
Anyways, I'm sure it's either not supposed to be Deflectable, or if it is, it's only supposed to take one tick and actually reflect it. Apparently grounding totem can take all the hits as well (if it's glyphed).
I'm sure this news is pretty old, but I've been out of raiding for a bit... so you're stuck with my ramblings.

