Moving the coax cable right at the plug sent SWR from 1:1 to infinite. This is a sign either of a short or a broken connection.
Heated the soldering iron and found out two things:
- it was a short caused by erroneous (criminal?) coax preparation
- the crimp-on section for the coax braid was loose and I could pull the coax out with no effort
Morale: if you care about your finals, check the plug assembling quality on your new magmount base!
Now I wonder how bulky the pseudo RG58 coax is! Will do some measurements soon.