Custom data fails to pull through to reports

I've marked this as critical, as it affects the outcome of reports, and therefore can affect funding applications and reporting for organisations.

Although data is not pulled through if it's legacy data in the contact custom fields, If the contacts custom fields are populated after the upgrade, there are notices shown throught the UI.

I've gone for reproducing the notices here: 

• use the 'Participant (List) report on d46.demo
• add columns (all 3 from 'Constituent Information') 
  • Constituent Information > Most Important Issue
  • Constituent Information > Marital Status
  • Constituent Information > Marital Date
• populate a contact from the report results with custom info in the above fields (I chose the top participant Nicole Adams
• re-preview the report

Expected behaviour:

• report shows newly added info

Actual behaviour:

• most information is not shown (the Marraige Date is)
• civi shows notices

Error message

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Notice: Undefined index: Edu in CRM_Report_Form->formatCustomValues() (line 2061 of /srv/buildkit/build/d46/sites/all/modules/civicrm/CRM/Report/Form.php).

*

Notice: Undefined index: M in CRM_Report_Form->formatCustomValues() (line 2061 of /srv/buildkit/build/d46/sites/all/modules/civicrm/CRM/Report/Form.php).

The error messages are not shown if the data was legacy (from before the upgrade), but is missing from the report.

Rolling back to 4.6.30 (that's what the original site was updated from) fixes the problem, but there don't appear to be any changes in drupal/sites/all/modules/civicrm/CRM/Report/Form/Event/ParticipantListing.php  - thanks @seamuslee