You can see in the image that there is a JMS bridge connected that has no active bridging, no configuration and is connected since before the router was started. It does in fact survive a failover to the STANDBY node. I got rid of it by switching to STANDALONE and then halting the entire router, it was gone on restart. But I suppose this should not happen.
Sadly I can't remember. It was more than 2 months ago that I disabled the bridge, I can't recall the exact circumstances. I just noticed it yesterday as I made some other changes that there was this strange active connection hanging around.