Supermodel can’t know what characters are meant to be in a URL

ah, ok

Not necesarily. It could make a reasonable assumption that if it reaches a character disallowed in a URL (typically: <>"{}|\^`()[]'), then the URL has come to an end. In this case, the ) could reasonably be treated as an indicator that the URL has ended. Similarly, 'http://example.co.nz' ought to exclude the trailing quote mark from the link, since the ' character is not allowed in a URL.

So not a bug, but it could be made a bit smarter.