Plague bug
Plus the stability factor is buggy in the extreme. Been knocked off cliff ledges i the past month or so after i popped Plague. Looking at the combat log to see what had happened, on a load of occasions Iv hav been feared and hit by Illusionary Wave (mesmer greatsword skill) both theoretically imposable if stability is already well up.
ps I was not hit by corrupt boon and the stability was not removed.