Are you moving off the record? That should be the only way you get unwanted records. If in the pic of your table I could see the editing icon for the record selector (far left) I'd say you're looking at an unsaved record (one that is in the process of being created). One solution would be to use form BeforeUpdate event to cancel or not. Another would be to ensure that whatever companion/related fields to this selection are required. If not, you'll get a prompt and won't be allowed off of the record, which in turn won't save it. Esc would cancel the record, but if you think that's not intuitive enough for users, you can buttons to save or not, or trap the error and present your own messages with response options. Many ways to prevent this and it has nothing to do with the combo properties except for one - control source property. If there isn't one, it's not bound so this doesn't happen. If there is, this is just the way it has always worked.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.