GIF restarting when clicking on a layer

Hi all.

I've got an animated GIF on the base layer of a slide with 8 shapes that have triggers to show layers. For some reason when I click the first shape to show a layer (regardless of which one I select) the GIF reanimates. It only does this when I click the first one - it doesn't happen when I click the others (again, regardless of which order I click them in).

Seems like a bug to me, as there's nothing in the layer settings that could cause this. 

The Storyline file is attached.