notice when removing group field from a content type set as group type

Errors thrown;

    Notice: Trying to get property of non-object in og_field_delete_instance() (line 660 of .../sites/all/modules/contrib/og/og.module).
    Notice: Trying to get property of non-object in og_field_delete_instance() (line 660 of .../sites/all/modules/contrib/og/og.module).
    Notice: Trying to get property of non-object in og_field_delete_instance() (line 660 of .../sites/all/modules/contrib/og/og.module).

Steps to reproduce;

1. create a content type, check the "Group" checkbox under Organic Groups
2. go to manage fields and delete 'Group' upon confirmation of deleting you receive the above errors

Setting as minor as everything appears to cleanup correctly in the content type regarding og settings etc. and this would only be seen by an administrator.