[Edi]

Thank you for the clarification. That also explains a lot of things. All units in the game have a unique identifier number that tells them apart from all other units and allows keeping track of afflictions, age, paralysis etc.

The unique monsters obviously also have these identifiers, and when they are resummoned, they will retain the characteristics they had previously (except maybe experience, which is afaik nullified). Seems that there is no similar nullification for paralysis, so when the unit dies and has the paralysis characteristic set to some value, it persists after the summon. So while it is a bug, it seems to be consistent with the game mechanics and not some totally bizarre behavior. I will amend the bug description.