guassian and radial blur create edges on layers

Hi community,

When I apply guassian or radial blur to shape a layer, the blur will cut off at random edges. I've attached an example image of a Ben Marriott tutorial project I've been working on which demonstrates what I mean. 

I have tried expanding the scale of the effect itself using the bounding box, I have also tried maxing the effects quality. Neither have appeared to help.

Any suggestions would be greatly appreciated. cheers.