When trying to delete bases in end loops, the “delete base” tool gets stuck and the end-loop has to be deleted manually from the sequence.
Hi dicey, I think what you are referring to is the length 1 hairpin, which is any hairpin smaller than three nucleotides. These hairpins used be in the puzzle maker, but the shapes were impossible to stabilize. Over time I saw that the dev just put a block on it, but that was some time ago.