client calling shutdown causes repeating error "channel 3: open failed: connect failed: Connection refused"

[howff]

Symptom: server window is filled with repeating messages (several times per second):

channel 3: open failed: connect failed: Connection refused

How to reproduce:

ssh -L PORT:localhost:PORT serverhost
% Rscript -e "remoter::server(port=PORT)"

RStudio:

> require('remoter')
> remoter::client(port=PORT)
remoter> quit()
> remoter::client(port=PORT)
remoter> shutdown()
>

After the shutdown() the server exits (client killed server) and then the messages start. You can logout from the serverhost (messages stop) and login again (to recreate the ssh tunnel) but the messages continue! The only way to stop them is to exit RStudio.

Using exit(client.only=FALSE) has the same effect.

(Separate issue, and worse, if you attempt to use client() now then the whole RStudio session totally hangs and cannot be killed!)

Environment: client RStudio 1.4.1717, server R 4.1.1, freshly installed 'remoter' package (0.4-1) from github on both ends

See also: https://github.com/RBigData/remoter/issues/25#issuecomment-658849466