Hello allan, hope your both well, yes it was a few years ago now, the "plastic bag" was about six foot out down the far end about four inches in diameter, i thought it was an alianthos carrier bag and went to get it out of the sea, then i realised! didnt get stung, i was too quick to get away!but as you say its very rare in that area, never seen one since, he must have been lost on the way home from ostraco or something!
might see you soon?
Barny.