User registration form is attempting to submit on first view

The standard Drupal /user/register form is showing validation errors due to blank fields even though the submit button has not been clicked.
Tracing through the code does indeed confirm that a submit is being attempted. Turning off CiviCRM module fixes this behavior.

I was also able to fix the behavior by editing civicrm.module:

case 'register':
$config =& CRM_Core_Config::singleton( );
if ( empty( $_POST ) || $config->userFrameworkVersion < 4.7 )

{ return civicrm_register_data($edit, $user, $category, true, false ); }

else

{ return civicrm_register_data( $edit, $user, $category, false, true ); }
return;

to read:
case 'register':
$config =& CRM_Core_Config::singleton( );
if ( empty( $_POST ) || $config->userFrameworkVersion < 4.7 ) { return civicrm_register_data($edit, $user, $category, false, false ); } else { return civicrm_register_data( $edit, $user, $category, false, true ); }

return;

...but I suspect this breaks other things, so I won't bother writing this up as a patch. Hopefully it helps clarify which conditions this occurs on though.