Anytime you're damaged by any other ability you're interrupted. For no reason what so ever should each tick of a DoT lose the ability to interrupt you. So, assuming you're working cooperatively with your team, the DoTer in question should be disabled and you cleansed. Chances are, since being dotted up and unable to cap is what drove you here, the odds of the match probably weren't in your favor anyway.
If it you helps you work it out, pretend it's not a DoT, pretend it's a group of little ugnaughts, tugging on your pant legs, but you can't shock them into oblivion because you can't find them..they're too small and wily. Oink.