Cannot create Survey if Events have 'is required' custom data

This is an issue with 4.7.6 and its reproducible on the Drupal 7 demo site.

1. Create a custom field called 'X' for Events that is required
2. Attempt to create a Survey via civicrm/survey/add (enter values and press 'Continue')

Step 2 fails with the error 'X is a required field'

The issue can be fixed by changing line 83 of CRM/Campaign/Form/Survey.php ...

$this->set('type', 'Event');

to

$this->set('type', 'Survey');

This change fixes the problem, but I'm unsure whether there is a deeper issue.

The form that is used by civicrm/survey/add is CRM/Campaign/Form/Survey/Main.php. The parent form is CRM/Campaign/Form/Survey.php. The possibly deeper issue is that the preProcess function of both forms (Main.php and Survey.php) deals with Custom Data.

I feel the child form (Main.php) should leave it to its parent to deal with Custom Data. But I think someone from the Core team might need to look at that.