Just recalled...
an interview for a junior sysadmin role a good while ago where the interview got to a networking question. They had a [Linux?] load balancing cluster with the front end rewriting the destination (public service) address to one of the cluster members (rfc1918) addresses and the reply, from the scrawled diagram, appeared to leave via another system/device. Apparently wasn't actually working. After exhausting my store of potential reasons - some from the rocking horse shit* category - I was flumoxed. The interview ended.
Only on the my bus back to the motel did the thought arise that I had assumed these network types knew that NATed traffic must be routed symetrically or the two devices that modify the address/ports must comunicate, or at least agree on, the mappings. I suspect they did not.
The whole experience was quite surreal.
* as in rare as....