In edit mode, if I highlight and click the paperclip with a line through it, in the editor it is unlinked. But as soon as you save it is lined again. Removing the code in code mode does not work either.
Are you talking about linked text or a full URL in the message body? The unlink option seems to work as expected for linked text.
Full URLs are automatically converted into links when posts are saved. As such, the unlink option will appear for them if you edit the message, but it will be converted back into a link again when it is saved. I can see why that might seem unexpected, though it can at least be worked around with [plain] tags.
Click edit, highlight it, and click the unlink button, it is now plain text. Click save, it is a link again.
I see what you are saying but that is not intuitive. If the button is only made to unlink a word and not an actual URL it should not show on URLs. So maybe they can fix that part. Or maybe unlink can add the PLAIN code.
As noted the unlink behaviour doesn’t (and couldn’t) override the auto link behaviour on save.
There are even valid and common use cases where this is the desired behaviour.
If you previously made a link into a URL manually, you may want to remove the link and allow it to be handled on save because that’s when it would auto link the URL into an unfurl or a media embed - a link created in the editor before save would prevent that.
As ever to prevent behaviours like this, we have the PLAIN bb code.