I've been lobbying people to complain about it for years now, as many Pinboard users find it deeply frustrating.
edit: and this was using the 'popup with tags' bookmarklet from pinboard's howto page 
It overrides the default "add bookmark" shortcut (Ctrl+D/Cmd+D), which is very nice if you have built a habit of pressing that every time you find something interesting.
By contrast, somehow, Mediagoblin intends to federate in a searchable manner, as I understand. But, I don't know how that's going to work.