Javascript error on Kanban board when pressing escape while releasing a Version

Steps to reproduce:
1. open a GreenHopper Kanban Board;
2. click Release;
3. type a name
4. click release.
5. press escape or cancel just after
6. observe the Javascript error

I was reliably reproducing this, but now for some reason cannot. Workaround for now seems to be not to use Firefox when releasing.

An error occurredHide…

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Details

        Exception: TypeError: this.element is null
        Resource: https://jira.atlassian.com/s/en_UK-ou3pzi-418945332/853/6/1/_/download/superbatch/js/batch.js
        Line: 2543

Environment
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:19.0) Gecko/20100101 Firefox/19.0

If the issues are still appearing, verify that the Work Sub-Filter is set to fixVersion in unreleasedVersions() OR fixVersion is EMPTY.