Warning, pass-by-reference

Warning: Call-time pass-by-reference has been deprecated; If you would like to pass it by reference, modify the declaration of [runtime function name](). If you would like to enable call-time pass-by-reference, you can set allow_call_time_pass_reference to true in your INI file. in og_subgroups/og_subgroups.module on line 246

line 246: og_subgroups_form_add_audience($form_id, &$form) in function og_subgroups_form_alter($form_id, &$form)

I'm sorry, but I don't know how to reproduce this warning.
It's the third time I got it in the homepage. When I refresh the page, it disappears.
I'm not going to enable call-time pass-by-reference. Are you going to fix it? ;)