That's a distinct problem (and new with 11.3 IIRC), and it affects everyone equally AFAIK--the part that's highlighted isn't what the system thinks it is. There's an open ticket for this (
https://jira.ixsystems.com/browse/NAS-104469), but judging by the activity from the devs, they don't much care. IMO, though, it's as I said above--if you're doing anything that calls for copy/paste in the web GUI's shell, you're just using the wrong tool for the job. SSH in instead.