Cysts showing up on frames that already had them popped before.

I don't know if there was a change in the system or if a new bug popped up, but for whatever reason previous frames I've used that had cysts on their neck popped somehow have been infected again. I specifically remember multiple times on frames I've used to farm with had cysts that kept popping up a week or so later. I thought only Nidus and frames that never had cysts are supposed to be able to be infected?