Move Message with Attachment from one Mailbox to another problem

Question

Hi,
starting with Exchange 2013 we have following odd thing. 
(That happens with Outlook 2010 aswell as Outlook 2013). 
My mailbox has several other mailboxes mounted aswell. (using Full Access at ECP Settings), aswell as one separate Exchange Mailbox with own User/Password. 
Now, when I have an Email with an attachment (like Word, .jpg, whatever), I used to move it to another mailbox by using "drag & drop". 
The mail was moved to the mailbox without noticable changes. 
Starting with Exchange 2013, the Mail is changed into Rich Text. That means, the attachment now appears somewhere within the message, instead as real attachment. Some attachments are also lost, and as the message was moved, the only way to recover it is
using our external Email Archive. 
Is this a bug, or didn't I see any option that results in this odd behaviour?
Moving to a different folder does work as expected, but not to another mailbox.
Thanks
Patrick 

Answer 1

Based on some research we have decided to create a workaround as all mails got converted from HTML to Rich Text when moving from User Mailbox to a PST(Archive).
We have built an add-in for end-users to archive based on the following Outlook-VBA
Option Explicit
Sub MoveToFolder()
Dim objApp As Outlook.Application
Dim strPath As String
Dim objNS As NameSpace
Dim objFolder As Outlook.MAPIFolder
Dim olCurrExplorer As Outlook.Explorer
Dim olCurrSelection As Outlook.Selection
Dim olCurrMailItem As MailItem
Dim m As Integer
'pick destination folder
Set objApp = CreateObject("Outlook.Application")
Set objNS = objApp.GetNamespace("MAPI")
Set objFolder = objNS.PickFolder
'get selected mails
Set objNS = objApp.GetNamespace("MAPI")
Set olCurrExplorer = objApp.ActiveExplorer
Set olCurrSelection = olCurrExplorer.Selection
For m = 1 To olCurrSelection.Count
Set olCurrMailItem = olCurrSelection.item(m)
On Error Resume Next
olCurrMailItem.Move objFolder
If Err.Number <> 0 Then
With olCurrMailItem
' due this week flag
.MarkAsTask olMarkThisWeek
' sets a specific due date
.TaskDueDate = Now + 3
.FlagRequest = "Call "
.Save
.FlagStatus = olFlagComplete
End With
olCurrMailItem.Move objFolder
End If
Next m
End Sub
for us it was important to have the mails still in HTML Formats as some customers are sending embedded images in the mail-body which are removed when the mail where converted to Rich Text.
For people who doesn't care in which format an mail gets archived another workaround is to Flag the Message with an follow up action, then unflag (complete the follow up) and users are able to move the messages but still they would be converted from HTML
to Rich Text.
Strange enough that with a simple VBA move event the message will stay in HTML Format we are happy to found a solution and maybe someone else can use it.