Submit-button disappears using HTML5-viewer

When viewing a specific course on an iPad, the Submit-button on the question-slides isn't visible.You can only see some parts of the button's corners.

In Firefox, is does work like it should. I tried another course, but that one does work fine.

I tried:

- Using the default player

- Using another customized player

- Applying a different slide master layout to the question-slides.

But it all didn't work out... Anyone familiair with this kind of problem?