Slide master and other layers

Good afternoon,

Apologies for the vague title.

I'm completely stumped by another issue I'm experiencing.

I've got a slide that shows a layer when the timeline starts on the base layer.

I've also got a slide master that shows a banner with a button to show another layer on the slide master to display contents. There's also a second layer that hides the contents layer.

The issue I have is when I click the button to show the master's layer, it hides the layer on the main slide and displays that slides base layer. When I click to close the master slide layer, I can't find a way to show the main slide's layer again. Or to keep the layer on the main slide visible.

All help for this gratefully accepted. 

I've uploaded a cut down version of the project with the offending master slides and other slides.

thank you

Karen