Mail: removing ics attachments deletes entire message text

This problem has been bugging me for a long time, long before Mavericks, but since there's no other place to post it, here we go.

Now and then I receive email messages containing text plus an ics (calendar) invitation as an attachment. After accepting (or rejecting) the ics event, I normally want to remove the attachment from the message and store the message in a mailbox for future reference. However, removing the attachment inevitably means that the entire message text also disappears! I am left with a message saying that the attachment has been removed manually, and nothing else. Which is not very useful for the intended future reference. I have no indication left on what the message was about.

Since this little procedure (reading, accepting/rejecting, removing attachment, storing) seems to be a very normal way to deal with such messages and invitations, and since I haven't found any reports of my specific problem here in the forum, I deduct that there's something wrong with my settings, and has been so for ages.

Any ideas or tips?