At my company we have a customer, on whose instance the HTTP proxy replaces the value of the "X-Jenkins-Agent-Protocols" header by the empty string. In such case Remoting 2.60+ is unable to connect, because none of protocols gets accepted.
I would like to add a new system property, which allows disabling the cache on supported protocols. It is not a problem solution, but it should be a good workaround in some cases. It would be also useful to improve diagnostics of such cases.