Well, to test out whether it could handle lots of items without encountering the bug, I created only one list. Later on, the uncertainty of not knowing whether an item is being saved made me create a second blank list.
Eventually as soon as I moved to the other list, at first it was blank, but after trying it again later on, I notice the list copied the previous contents of the original list. I knew it copied it because the list only had the contents of the older entries so it didn't move the 3 newer checkboxes of the original list with it.