It is possible simultaneously check "Create New" and "Update existent" check boxes during multi value import

1. Create simple custom files with "Alphanumeric" type of field (Custom Filed->Student->Select "Alphanumeric" type)
2. Navigate to the Import Multi value page and upload 'csv' with ID and valid text field value (ex: 128, test)
3. Assuming that some mapping have been created before (Field Mapping)
4. Move to second page of the wizard (Update this field mapping and Save as a new field mapping)
5. Check both check boxes

Actual Result:

Notice: Undefined offset: 0 in CRM_Contact_Import_Form_MapField->buildQuickForm() (line 517 of /var/www/sites/all/modules/custom/civicrm/CRM/Contact/Import/Form/MapField.php).

Expected Result:
If I checked one check box another one have to be disabled and vise versa (or at least absence of error)