Sub Rogue Damage

Something is wrong with Sub damage.
I tested on dummy sometimes my backstab hits for 37k (ilvl 506) and sometimes hits for ~ 52k. I think the problem is with Glyph of Hemorrhaging Veins its probably not working all the time.

https://www.youtube.com/watch?v=45ahT6qK4yA#t=5m32s this guy damage on dummy is much more than mine and my gear is a little better, even when I use same glyphs and rotation and all.

http://i.imgur.com/v3bOsCy.jpg
http://i.imgur.com/ld5DfNy.jpg
http://i.imgur.com/po8ZpqB.jpg

That's after using the pvp trinket and engineering gloves enchant and all cds.