edit saved draft, attachment sent 0-length

Anyone seen the following odd behaviour:

User1 creates mail and adds attachment, saving it as a draft.

User2 (using proxy) edits the message body and does NOT edit the attachment. He saves the attachment on the desktop to view with a separate application. Then either re-saves or sends the mail - at this point the attachment becomes zero length but is still listed as an attachment.

This does not happen every time but is fairly frequent. I do not know if proxy is a key factor here or not. If User2 does NOT save the attachment to the desktop the problem does not seem to occur. Another symptom we see is sometimes separate instances are created for each subsequent save of the draft leaving a trail of versions, but again this does not always happen and I am not sure if its consistent.

Just to repeat, user2 is only editing the body and not editing the attachment, just saving it.

We're using GW14.0.1. Ideas anyone?