Prism beam stuck open

Hey all 

I have a Mac Martin  fixture in my Augment space, all attributes work correctly except for the prism. The prism is automatically inserted into the beam and I can not find a way to remove it. If I open a new show file, it will work as normal, but for some reason, this show file has it inserted.  

Where should I be looking to fix this issue? 

Thanks in advance 

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