Disappearing Navigation buttons

Hi,

I added some custom arrow buttons to my skin to replace the current previous and next buttons in the arrow bar. For some reason, they will not display. They're the same size as all of my other buttons, and they all show up without incident.

When I generate, I selected "Manually" in the "Syncronize Table of Contents"  section of the properties, hoping that would help, but no luck. Those arrows just won't show up. Any ideas?

I'm using RH8.

Thanks!