Vector blur through transparent material

I searched, but didn’t find anything.

I’m making a propeller type thing with vector blur. It works fine, but as soon as I surround it in a ‘glass’ sphere, the vector blur seems to have no effect. (Material uses ray transparency).
Is this a known problem? Is there a workaround?

probably because vector blur uses the depth buffer and the propellor is occluded by the panel.

render in different layers and combine in the compositor.

I was afraid that was the only workaround:o. Oh well. Thanks for reply.