When trying to use the preview function (and when typing in this comment field) my javascript error console is spammed with

Timestamp: 29.06.2012 09:27:01
Error: can't convert undefined to object
Source File: http://tickets.musicbrainz.org/s/471/1/1.0/_/download/batch/jira.webresources:jira-global/jira.webresources:jira-global.js
Line: 9

and

Timestamp: 29.06.2012 09:27:24
Error: jQuery.fn.isDirty is undefined
Source File: http://tickets.musicbrainz.org/s/471/1/1.0/_/download/batch/jira.webresources:jira-global/jira.webresources:jira-global.js
Line: 9

I'm using Firefox 13.0.1 on Linux, it does not happen in Opera 12.00