XF 1.1 "Upload a File" button missing?

I have the options set for file size, file extensions, dimensions, etc. under Home>Options>Attachments. However, my forum members are reporting to me that they don't see a "Upload a File" button when they are adding a new post.

I can see it on my screen. I see all three buttons in a row: Post Reply / Upload a File / More Options... but my forum members don't see the middle "Upload a File" button. They only see: Post Reply / More Options...

Any ideas?