Attachment of received email is not attached to the created Document (ToDo)

Frappe Framework
1

Hello,
i have created an email-account, which can receive emails and which creates a ToDo for each incoming email.
So far so good.
But if the received email has an attachment, then this attachment is NOT attached to the ToDo Document.
How can i achieve, that the sent attachment gets attached to the created Document?
Normally this should work out of the box… What am i doing wrong?

Thanks in advance