Unable to select auto-complete result in User Picker custom field

Summary

Unable to select a value from User Picker (single user) custom field in JIRA 6.3.15

Environment

JIRA 6.3.15
JIRA Agile 6.6.60, 6.6.70

Steps to Reproduce

1. Create a User Picker (single user) custom field
2. Associate it to the Default Screen
3. Navigate to an Agile Board, click the Create button to trigger the pop-up window
4. Enter some value to trigger the auto-complete
5. Try to click any user from the result

Expected Results

User is able to select the auto-complete result

Actual Results

User is unable to select the auto-complete result

Notes

If the action is performed from an Agile Board view, this javascript error will be thrown:

An error occurred
Please try refreshing the page, or contact your administrator / Atlassian Support if the problem continues.
Details

1. • Exception: Uncaught TypeError: Cannot read property 'match' of undefined
   • Resource: http://levi:9485/GHS-16485/s/37a5face8b9ec703a9e403451c82e5aa-T/en_UK1l2k1r/6346/2/502b2516d7167bb75064a9c1139d6d41/_/download/contextbatch/js/greenhopper-rapid-non-gadget,atl.general,gh-rapid,jira.global/batch.js?locale=en-UK&isAdmin=true
   • Line: 8420
   • Column: 25

1. • Exception: Uncaught TypeError: Cannot read property 'match' of undefined
   • Resource: http://levi:9485/GHS-16485/s/bc4dfeb5e5b23f34060762ab22034a42-CDN/en_UK1l2k1r/6346/2/25/_/download/superbatch/js/batch.js?locale=en-UK
   • Line: 11051
   • Column: 13

Environment
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.115 Safari/537.36

Stack trace

• TypeError: Cannot read property 'match' of undefined
• at JIRA.Forms.CreateIssueModel.JIRA.Forms.Model.extend.isCustomFieldId (http://levi:9485/GHS-16485/s/37a5face8b9ec703a9e403451c82e5aa-T/en_UK1l2k1r/6346/2/502b2516d7167bb75064a9c1139d6d41/_/download/contextbatch/js/greenhopper-rapid-non-gadget,atl.general,gh-rapid,jira.global/batch.js?locale=en-UK&isAdmin=true:8420:25)
• at JIRA.Forms.CreateIssueModel.JIRA.Forms.Model.extend.normalizeCustomFieldId (http://levi:9485/GHS-16485/s/37a5face8b9ec703a9e403451c82e5aa-T/en_UK1l2k1r/6346/2/502b2516d7167bb75064a9c1139d6d41/_/download/contextbatch/js/greenhopper-rapid-non-gadget,atl.general,gh-rapid,jira.global/batch.js?locale=en-UK&isAdmin=true:8433:17)
• at JIRA.Forms.CreateIssueModel.JIRA.Forms.Model.extend.markFieldAsDirty (http://levi:9485/GHS-16485/s/37a5face8b9ec703a9e403451c82e5aa-T/en_UK1l2k1r/6346/2/502b2516d7167bb75064a9c1139d6d41/_/download/contextbatch/js/greenhopper-rapid-non-gadget,atl.general,gh-rapid,jira.global/batch.js?locale=en-UK&isAdmin=true:8397:24)
• at HTMLDivElement. (http://levi:9485/GHS-16485/s/37a5face8b9ec703a9e403451c82e5aa-T/en_UK1l2k1r/6346/2/502b2516d7167bb75064a9c1139d6d41/_/download/contextbatch/js/greenhopper-rapid-non-gadget,atl.general,gh-rapid,jira.global/batch.js?locale=en-UK&isAdmin=true:8729:37)
• at HTMLDivElement.jQuery.event.dispatch (http://levi:9485/GHS-16485/s/bc4dfeb5e5b23f34060762ab22034a42-CDN/en_UK1l2k1r/6346/2/25/_/download/superbatch/js/batch.js?locale=en-UK:3340:9)
• at HTMLDivElement.elemData.handle.eventHandle (http://levi:9485/GHS-16485/s/bc4dfeb5e5b23f34060762ab22034a42-CDN/en_UK1l2k1r/6346/2/25/_/download/superbatch/js/batch.js?locale=en-UK:2949:46)

Workaround

1. Create issue normally without selecting the User Picker value. Edit the issue afterward, to update the field
2. Fill in the username without selecting the auto-complete result
3. Access the create issue screen in http://your.jira.com/secure/CreateIssue!default.jspa . The User Picker custom field is working correctly there