According to description:
‘Your Bleeding damage is increased by 15% [x] of your Vulnerable Damage Bonus.’
My VDB from Starts&Materials - 209.7%, hemorrhage should add x31%. Current bonus showing x26% (correspods to 173% VDB)
26% is correct according my calculation.
How Vulnerable Damage (VD) shown in Stats & Materials is calculated?
Say we have +x % vulnerable damage from items and paragon boards.
VD % = 1.2 * (100 % + x % - 20 %) - 100 %
Say we have for example x = +70 % from items and paragon boards:
In his case VD % = 1.2 * (100 % + 70 % - 20 %) - 100 % = 80 %
From that equation you can determine what x really is:
x = (VD + 100)/1.2 - 100 + 20
x is REAL VULNERABLE BONUS (without default 20% multiplicative value)
So in your case: VD = 209.7 %, you get for x:
x = (209.7 + 100)/1.2 - 100 + 20 = 178.08 %.
Legendary node Hemorrhage grants 15% from your Vulnerable bonus damage (x).
So … 0.15 * 178.08 % = 26.712 %.
So … I guess in-game calculation is correct 
lul, haven’t checked forums for a while.
First, ty for so detailed answer.
Second, with your formula it also means that without any +vulnerable it will be -4% VD which not seems good 
third, in-game descriptions are often a BS as most of its code. But will not blaming devs, cos overall D4 profit concept seems is not about selling descent gameplay
I have 1k+ vul dmg but hemorrhage bonus is at 122% instead of 150% was working well before 1k when i still had 800 vul dmg