Pincushion urchin taking my Feather Duster on a rollercoaster ride

One of my pincushion urchins got my Feather Duster stuck onto its spines
yesterday. The feather duster didn't seem too put out to start with and
was extended for most of his trip around the tank - eventually he
retracted for a bit longer than normal so I "rescued" him and
repositioned him in the tank, away from his original position and far
away from the Urchin.

This morning, I noticed that the Urchin had found the Feather Duster,
and the FD is now firmly on the spines of the Urchin and off on a trip
again. He is, like yesterday, extended with feathers swirling around as
normal.

So my question is whether these trips on the back of the Urchin are
going to harm or damage my FD? Should I keep unattaching him or should I
just leave well alone?

TIA
Gill