@PuddinHead, My Costco shopping list (and many other lists) work just like yours. I also have many other one-time lists that work the normal way, and checklists work fine for these.
@Boot17, On my android version, the bulleted lists with checkboxes always get converted to checklists when I add an item to the bottom of the list. However, the method works for numbered lists and seems to stick better. I notice that it also works for checklists (i.e., add a checkbox to the selected checklist, and each item in the checklist gets a checkbox in addition to the checklist box). This might be the useful for some lists, if you can remember which of the 2 boxes you want to check.