Oh, that is a BAD design.

Drew has a sweater. It has a zipper. The zipper can go up when the tab is not pulled out, but can only go down (to come off) when it's lifted out, so it doesn't slide open by accident.

If the tab comes completely off, it is treated as in the "flat" position and the zipper can't go down.

Luckily, it was only a couple inches from open when we discovered it was stuck after the tab came off, and Drew was able to get out of it without it needing to be unzipped. And now I know I can trigger it with an unfolded paperclip and how, but really people? If the zipper tab comes off you need a paperclip or scissors to get the sweater off if it's fully zipped up, because the neck probably wouldn't fit over the head that way? Not cool.