Ah Mcknuckle, yet another misinformed person about DVP. I've explained all this before, and I'm sure I'll have to explain again.
To start off with, the DVP check is indeed 100%. The 0% is just the base aura that sits on the engi, means nothing really. http://auno.org/ao/db.php?id=154715 Click that, then scroll on down to "On Use" and click that link. You'll see http://auno.org/ao/db.php?id=154701 Notice the 100% check? That's the hostile part.
Now once again if you refer to that second link, take a look at the break on attack chance, the break on debuff chance, and the break on nano chance. They are all 100%. And yes, it does break on dmg shields and reflect damage. I can demonstrate this in a fraps if you like.
The fact that you've seen it not break is actually true however, and it is a bug. When too many things/people are hitting whatever target DVP is on it bugs and stays on. This bug is not unique to DVP however. Calms and the MP mez pet experience the same thing. Ever seen a stuck calm? It's because too many people hit the calm at the same time. The mez pet really perma stuns mobs (until a higher stacking "calm/stun" lands) which makes inferno hards f/e ridiculously easy. Now before you get all bent out of shape about engineers exploiting this bug, it can IN NO WAY be made to occur solo, on my eng at least (I've tried). I can very occasionally and mostly by accident get the mez pet to bug it's mez solo when I use SS+me swinging+Rihwen hitting. When I dual log my crat and MP f/e though, the mez pet perma bugs it's mez and the same happens when I dual log with my eng with DVP. I can again demonstrate this in a fraps if you like.
What sort of equivalent def ratings do you think engineers are sporting when they blind someone with DVP? If I maxed evades on my engi and added all my aad from equip I'd have about 1800-1900 static def rating without DVP. So that means with DVP I'd be 3k-3.1k. Is your def rating higher than that on your MA? Do you get hit? How many professions do you think can perk 3.1k def ratings at tl7? Doing an evade setup on an eng based around DVP would be pointless because the first time your hit you'd lose 1/3 of your def rating, and you'd have given up a ton of hp gear.
Sure we can switch after fight. Still doesn't mean auras/procs aren't bouncing our ncu around and we could missclick something. But frankly, I'd rather just use NSD all the time anyway versus trying to spam DVP which will last maybe a second per cast on fighting targets in the first place. Saves me the trouble of accidentally turning off important buffs while I'm at it.