Jam

Hence the peanut butter and jelly problem.

Even though the technical term for jam made from fruit juice may be jelly, it isn't really used as an everyday term. In the supermarket, on the "jam" shelves, you might see a jar marked as "bramble jelly" "apricot preserve". At breakfast in a hotel you would be offered a selection of jam and marmalade.

Post Script: I've just remembered another category of jellies, eaten with savoury foods.
Q: "Would you like jam with your lamb?"
A: "Yuk"
Q: "Would you like jelly with your lamb?"
A: "Yuk"
Q: "Would you like redcurrant jelly with you lamb?"
A: "Mmmm, quite possibly"
So we do have the precedent of eating jelly but we choose to forget, possibly because we only hear "redcurrant-jelly", rather than filing it in our brain as jelly(redcurrant). I dunno.