Yeah, I agree with you. This has nothing to do with the kind of requests you are doing. I could reproduce this kind of behavior very easily locally with huge churn of connections with simple commands like isMaster. The leak is predominant, if I run a command like listDatabases. Probably we have more than one kind of leak.
On FoundationDB server, we periodically run Valgrind to catch memory leaks. We never ran it on Document Layer. I have raised an GitHub issue to track this particular issue - https://github.com/FoundationDB/fdb-document-layer/issues/202.