Avia Post nav prev/next buttons Behaviour

Hi Guys,
I’m having a bit of strange behaviour with the post next/prev buttons which slide out from the side of the page to go to the next post.

I’m using them here http://concretepoolsystems.co.nz/gallery/ (using portfolio items)
and on the ‘in construction’ page (using posts)

I can see the grey pop out arrows, but when hovered over they hide behind the blue body background colour/image.

Using a boxed version of the theme with a blue body background and the ‘light-noise png’

Have tried the css z-index for #top .avia-post-nav but no joy.

Chrome and Safari – using the enfold 2.7.1 and wp 3.9.1

Any help appreciated.

Cheers AL