Derek Lyons wrote:

When the thrusters were not supposed to ever be used again - and
indeed were supposed (IIRC) to be permanently deactivated years ago...

You're confusing Zvezda's engines with Zarya's engines. Zarya's engines
were the ones that were (I believe) deactivated after docking to Zvezda.
Zvezda's engines were always meant to be a backup to other boost
methods, even though they weren't needed for normal operations since
Zvezda docked to Zarya/Node 1 in 2000.

Then something is up and/or wrong when they test them 'to see if they
work'.

Why is this so strange? There was no particular reason to fire the
engines since Zvezda became part of the ISS complex, so they simply
weren't fired in that time. More recently, somebody decided to test them
out, even though there was no particular need for them.

I think the reason for conducting the test was probably entirely innocent.

--Chris