If in hudson my job name is "Job One", then when it writes a comment to JIRA for
the successful build #212, the link looks like http://www.example.com/Job One/212.

It should look like http://www.example.com/Job%20One/212

In otherwords, the URL needs to be URLEncoded before it is written to JIRA.

Workaround is to not have spaces in the Hudson Job name.