"Phantom" objects appearing when showing layer

Hi guys,

I wonder if you could help with a strange problem that's just started happening.

I have some buttons on my stage that, when click, reveal a layer containing 4 buttons for the user to select. Each of these buttons, when clicked, changes the colour of the base layer button, and hides the options layer. The problem occurs when this options layer is revealed. A light blue rectangle and line appear every time the options layer is shown, for every occurrence throughout the project. 

Other hidden layers display fine, but whenever a layer is displayed with this button options on, these random objects appear; same size, same colour, same position, every time, whether previewed, published, local or online.

I have checked and double checked and there are no objects on the stage that I'm missing. I also thought it could be something to do with "interference" coming from the feedback master slides (as the objects look like bits of a feedback slide; button and top edge) but the elements don't line up.

In short, I'm stumped! Below is an image highlighting the problem and attached the storyline file itself.

Any help would be greatly appreciated.

Thanks,

Andy