Not sure if it is a defect, i could not find anything about it.
Is the emails that are send out, there is a field tmpNewDoc="1"
Likely, this wil not give any problem if the mail is sent via SMTP but when it stays within a Domino environment, this field will also be on the received document, causing the 'Forwared' option to be hidden in the receivers Notes client.
I guess the field only has a meaning for the sending Notes client and not for the receiver, so likely, it should be removed before sending.