Bug - deleting a project DOES NOT delete the associated chats

I had a large number of discussions in a project that was starting to bleed through into responses in unrelated conversations, so I deleted the project (and therefore all of the discussions).

But it looks very much like this does not actually delete those discussions! Responses are still using the information in those discussions which I now cannot access to properly delete.

To test this, I created a discussion in which I claimed that I had an uncle named George Trueblood who was in the Royal Canadian Navy. I verified that the model could spit this fact back to me in a new discussion, and that after deleting both of the discussions, the model no longer knew (or believed that it knew, anyway) anything about my family tree.

I then created a new project, created a new discussion in that project in which I provided a similar nonsense fact about my family, then deleted just the project without deleting the conversation itself. ChatGPT is now convinced I had an ancestor named Matilda who was tried as a witch in Salem.

...is this a known thing? Is there a delay before these orphaned conversations get fully deleted, or a way to recover / purge them completely? I assume the nuclear option of "Delete All Chats" would work, but there are other chats that I'd like to save.