that image looks like that of a table with a sub datasheet. If I cycle record selectors on/off on a split form, they only show/not show on the single record portion and not the data sheet portion. I don't think I've ever seen + and - signs on a split form. I don't see record selectors in your image either. Taking all that in consideration, are you sure what you've posted is an image of a split form?
EDIT - if you said this was a sub form where the source object was a table instead of a query, and that table had a sub datasheet, then that might explain it. However, I don't think I have ever constructed that combination.