Hi Spam Fighter,
I can confirm that this is working as designed, without a filter AsyncOS would not scan the message body and therefore does not know if there are attachments or not. To enable logging of attachments, any filter that does body scanning will do, i.e. conditions like file name, attachment potection, etc. along with a delivery action will do. I suggest not to use any of the conditions that search for text in attachments, as they are quiet performance consuming (unless you actually have a use case for that).
Hope that helps,
Andreas
