Help - Bug on Lightbox Submit button

I am experiencing an issue with the lightbox interactions and the Submit button. I have 5 lightbox interactions in my Storyline file. The first few interactions work fine with the built-in Submit button in place. However, the last 2 interactions changed the built-in Submit button into the Back and Next buttons, when they are not checked off in the Properties. 

I am wondering if someone can help me on this and to determine whether this is a bug or something to be fixed. Thanks!