Mqtt broker bridge config is partly ignored

A bit hard to find the propper place for this, it is about Configuration, but none of the sub-categories fit. I saw another mqtt-related thread in Scripts&Rules and put my question next to it.

This is OH2.5.11 on a raspi 3b+ with openhabian, my setup makes heavy use of mqtt. File-based configuration of a Bridge with a handful of things and lots of Channels.

For the most parts everything works nicely, just one thing: I wanted to change the label of the bridge and add some properties (clientID, lwt*) and openHab simply ignores me at that.
Can’t even say that the file is ignored, I added and removed some channels down the file and those changes were visible in the paper-ui immediately.
But even after a clearing of the cache and removal of some entries under /var/lib/openhab2/config/org/openhab/ and restart of oh2 it still creates a random clientID and the bridge is listed under the other name…

So, here is the top of my .things - file:

Bridge mqtt:broker:mqBroker "mqBroker" [ 
    Thing topic sensors "mqSensors" {


So, is there a subtle flaw of my syntax which oh2 lets pass in a show of goodwill, just ignoring the flawed bits?
Where from does the system take the old config data? It even recreated config/org/openhab/mqtt.config after the restart. Should I try to edit that file?
Thanks in advance for sharing your experiences.

Interesting. This is a similar complaint from a while back:

Sounds like the workaround is to split the bridge from your things, into two separate files. An example is here in demo2.things: