I am the original author of the SSH extension.
Thanks for raising this issue. The SSH extension only supports running non-interactive commands, because interactive commands require a tty attached.
I've just tested with running vncserver but I get the expected behaviour: running vncserver (interactive command) will not show anything, and will return in ~1 second after the timeout.
After that, you can launch other requests. Can you supply additional details about the error (exact order of commands maybe)?
Regarding your suggestion to also add stderr to the message, as well as the exitStatus, this feature will be added in an later release.