In sci.electronics.design Tracy Hall wrote:
Thanks, all, for your helpful responses.

The general consensus appears to be that a tiny electric dipole will be
induced that oscillates transverse to the cable at the same frequency
as the carrier. It might possibly leak a tiny amount of energy to the
area immediately surrounding the coax, but probably not a significant
amount compared to that which is already lost due to imperfections in
the cable.

Hmm.
I suppose that for largish low frequency components in the signal, you
might also get the cable bits physically moving, both together, and in
relation to each other, which might screw up the impedance a little.