Trigger image state on base layer being lost on return

Sorry - that's the best descriptor title I could come up with.

On my base layer I have an image with two states: Normal and Layer seen (with a tick). This image is a trigger to show a layer. Once the user has seen the layer (on which there are mouseovers), these set a Layer seen variable to true.

I have a %Layer% text box that confirms this is working and the changed image displays through the layer (I do not have an option to hide this image in the layer - as it isn't visible in the first place, but I can hide this with a mask on my layer.)

My issue is that when I close the layer (I have a close button that "Hides layer", the trigger image returns to the Normal state - without the tick. My slide is set to Resume saved state.

Further, when I repeat the process and click on the image to show the layer again and then close the layer, the trigger image becomes invisible!