To make a popup layer sticky and have animation requires a workaround.

Remove the animation from the link that calls the menu layer
Cut everything from the menu layer and paste-in-place on the mouseoff layer (leave all the objects selected)
In Web Animations > Reveal/Scroll select your desired animation (leave all objects selected)
Cut the objects and paste-in-place back on the menu layer

If you try to add a reveal animation that is sticky whilst on a layer, Xara will tell you it can't be done...but it can.

You will have to hang fire for someone versed in the black magic art of coding to tell you how to make it disappear when scrolling, I'm just a peasant.