Going to app settings on master to add a new server, or add a new server from the server tabs, click on any input so you could write server name or url, use ctrl+v to paste anything thre is in the clipboard (you'll need to copy something first). Same thing using the menu->edit->paste
clipboard is pasted into input
I also noticed the same with ctrl+c from the developers toos when displayed, select some logs, ctrl+c, trying to paste pastes whatever was there before.
Most likely, we redirected all commands with this fix: https://github.com/mattermost/desktop/pull/1092