Alt text reverts to a space

I have the opposite problem from what is described in this post. 

I am reviewing and making accessibility changes to a series of courses created by other developers. In one of the courses, on the question slides, the alt text for the radio button answers is a space. I want the alt text blank, so the screen reader reads the text of the answer, as it does in other courses.

I tried deleting the space and saving, from both the Focus Order and the Accessibility tab on the Size and Position popup. When I open it again, the space is back. In other courses, deleting the alt text has worked--though I'm not sure whether it did for radio buttons.

Can I stop this from happening? I'm not looking forward to copying and pasting all of the answers into the alt text.