I 've decided to share my findings, failed to see if it has been brought up to this topic yet and my sincerest apoligises if I am just spamming it up, read through pages and pages and perhaps I am just blind but this happened with a fresh new game started after Patch 5 and Hotfix 16 was released so keep that in mind.

This was the route of massacrating Grove so had plenty of mingle with Minthara early in Act 1 and whether this had any weight I would not know, playing two thirds into Act 3 with Minthara as a companion (and as love interest), she took me completely by surprise when this one time
kissing her (before patch 6) in the elfsong campsite, there was suddenly a dialogue option to tell Minthara that this last kiss tasted funny and she went on to explain she had glaced her lips with poison.

With only three dialogue options to choose from I must of course have picked the one with least voice over lines, so I reloaded my game to an earlier segment and retraced my steps exactly the same leading to that kissing point and guess what I never managed to retirgger this scene, has anyone in this topic managed to see what actually triggers this whether its completely random or just buggy?

Reason it took me by surprise was because felt like it happened relatively early into Act 3 so I was nowhere close to reaching epiloque.

Post patch 6 I have kissed Mitnhara extensively through Act 3 again, every step of the way of doing side quests or uncovering new areas I would talk to Minthara and give her a round of kisses and same as before never managed to trigger it again,
it was not the same as the poison dialogue you get during epiloque now that I reached there with no results.