Suffering from success - Too much damage with Mamba? DoT Cap issues?

Hey guys,
I have been building my pathfinder Mamba around Celestial Mathematics + Pneumatic Daggers for massive amounts of flat cold added to mamba, and recently found an issue where i was doing no damage on most hits, and only every few hits would even do damage at all...

I suspected it was because i was somehow applying a poison before striking with Mamba, but nothing else could be doing that. Well after a bug report, a suggestion was to remove some damage supports and lower my damage below the damage cap... that works mostly, but now im trying to understand how the damage cap actually works, especially for Ubers.

Pobb is here https://pobb.in/UmEq5GE51ve5

Against pinnacles/guardians, my poison is 65m. This is over dot cap, so understandably trimmed to 35.8mill. But ubers have a 70% dmg reduction, and my poison dps is only 19.5mill (And caustic ground adding to bring it to cap).

So my question is: Does exceeding the dmg cap in a single poison instance prevent the damage from being applied at all? (i.e. it makes the integer completely overflow instead of capping)
Do multiple poisons avoid this by just having no affect for the ones above that cap (and the ones below still have a proper count)
Does the uber damage reduction apply differently for multiple poisons? I was under the impression it was 35.7mill AFTER damage reduction, rather than before, but maybe its the actual initial instance > capped > dmg reduction > capped again.

(I probably need to ask this directly to Mark on the forums in fact)