grey overlay on parent layer while mouse down (HTML5)

Hi

i have a layer container with several layered buttons in it.

on ipad when i use zoom buttons for example (in fact the ones that are defined with ondown actions) the parent layer is being overleyed in grey.

any idea on how to avoid this?

Thanks!

you can check it here : http://www.immersiveprod.com/inserm

try to keep mouse down on a navbar button on IPad, you will see the parent layer becomes grey.

regards