Currently axes bleed effect from Dual Blade and Blunt removes the 36% damage bonus from Ambush.
I tested and confirmed this and have submitted a bug report.
This is a real bug, please don't use axes if you rely on Ambush providing a boost to DPS as a DWer.
How it works - The first attack from stealth applies a 36% damage bonus to the follow up attack as per normal. Upon landing a swing or weapon ability the target begins to bleed and you will notice ambush no longer applies any damage bonus at all.
I have deconned my axes and made swords and everything is back to working normally. A costly problem as you can imagine. That's 4 purple deadric weapons with 4 legendary weapon glyphs down the tubes. Learn from my mistakes please!
Duuk