Broken Membership Detail reports

[WORC]

I've broken some membership reports after creating custom fields. I get this error message when trying to run reports based on the Membership Detail report:

Fatal error: Cannot redeclare CRM_Report_Form_Member_Detail::$_customGroupExtends in /home/sitename/www/www/sites/all/modules/civicrm/CRM/Report/Form/Member/Detail.php on line 49

Troubleshooting tried since getting the error:
The custom fields (used for memberships) have been deleted.
The related membership type has been deleted.

No other report types seem to be affected. Any ideas on a fix?

[Coleman Watts]

Does it only affect the saved report? Are you able to create a new Membership Detail Report from scratch?

[WORC]

No. Reports created using the "Create New Report from Template" screen also give me the same error

[WORC]

I was able to resolve this error message, but I can't really recommend this solution to others since I'm not sure if there will be any side-effects: I simply removed the text

protected $_customGroupExtends = array( 'Contribution' );

From line 49 of Detail.php.