Yeah that's not a bug, just the way things are. SE can create things in temp slots, but you're going to lose them all the same when the slot is gone, but as described on the part, sometimes a temp slot may require an extra bit of time before it really disappears because it's no longer supported. Best to just keep SE off if you're about to have an unstable situation, so that it doesn't produce anything under poor circumstances, or keep going and have it build something else after the fact... Temp slots are unstable by their nature.