cataclysm fire mage pve test for dungeons - what's the deal with combustion?

/ waylanderuspl
I've just started playing a fire mage for pve, so still learning, and without pefect gear, but here's a test of basic rotation damage output for cataclysm dungeons. What confuses me is unexpected combustion dot numbers, e.g. in the 0:37 of the clip I use combastion with all possible dots and all possible procs, that is: living bomb, ignition, pyroblast, power torrent, lightweave embroidery, volcanic destruction and i use soul casket, all of the active - combustion dot says: 4415 damage every second, but the second time I use combastion in 3:05 of the clip I have one less proc - all mentioned above without lightweave emroidery only, so in theory combustion should be lower but it says: 6169 damage every second... anyone can explain?