I am using the latest versions of RefinedStorage, MCMultiPart, and ThermalExpansion. When I attempt to use a TE cover on the RS cables, it will not attach. I can use those covers on TE pipes, just not RS cables. I was under the impression that RS supports MCMultiPart (I am also under the impression that TE uses MCMultiPart) and that something like this should work.

Is this a bug or am I doing this wrong?

I am also under the impression that TE uses MCMultiPart

You are under the wrong impression, TE doesn't use MCMultiPart for their covers.

Ok, then this explains why it isn't working. Thank you for clearing this up for me.