setMask doesn't work from within a symbol?

I’ve attached two files that are exactly the same except in Mask_symbol.fla I copied the frames from the _root and put them in a symbol.

When you open the files you’ll see the mask on the _root gets applied at runtime like it should but once you take the exact same frames and put them inside a symbol it no longer works.

The paths used to reference the objects are relative so i don’t think it’s a path reference issue.

Can anyone help?