Interesting. We are usually internally totally shielded from this bug cause we use pg bouncer, but we will have a look internally to see if we see similar leaks. 
Can you debug into the “connections” hanging there, do you have any info on what the last query is these stalled connections ran? how long are they stuck without running anything?
@tgxworld where is our official pg image with bouncer? we need a howto explaining how to use it.