Created, changed, source and campaign as columns
The column picker on the board and in the list offered the record's own details next to your fields: when it arrived, when it last changed, which source it came from, and whether it came out of a campaign. Selecting one did nothing. No tick, no column, no message.
The selection was stored correctly and discarded on the way back, by a filter that only recognised field identifiers and treated everything else as pointing at a deleted field. Both kinds of column now survive the round trip.