As far as I can tell
if you establish a "normal" PGJDBC connection then run this:
connection.isValid(5) on a server that "hangs" (it's hard to describe,
but for instance an amazon RDS Postgres instance that was working
before but has since been "stopped" -- I believe it is fronted by some
kind of load balancer).
It won't be interrupted in 5 seconds it will just hang forever,
despite the timeout directive...
Just reporting it here...
Cheers!