I got diseased in the rat barricade quest, and upon leaving the QA, my goblin PC was cured. It's not the first time this happens.

You may have just made your save while loading...will check it out though.

There is also a Bioware bug where you transition and it looks like you've recovered from a disease- hp bar goes back to normal, icon disappears, etc. You are still diseased though and the effects work normally.

Also, I can say that I have left that quest before whilst remaining diseased.