If you have two tabs open for editing product features on the same product, then they'll both show the "add to cart tweaks" as options in the pulldown menu. You can theoretically fill out both forms and submit them, and you end up with two "add to cart tweaks" features. Not very common, but I keep a whole lot of tabs open, and I accidentally did this.

Right now, doubles seems to be prevented by removing the option from the pulldown if it's already present, but this doesn't work in all cases, so I'd suggest doing a check before adding it, and perhaps overwriting the other if there's already one. Not a big coder myself, but thought I'd suggest :)

Great module by the way! Really helpful!