OfflineIMAP ERROR: list.remove(x): x not in list

[mightyape at gmx.at]

Hello,
I am trying to backup my Emails from a Exchange Server. I can authenticate, but then I receive an error after a few Emails.
 
I am using the Ubuntu Repository Version and I also tried the latest from GitHub (OfflineIMAP 6.5.7-rc1).
 
Here is the info output:
bash:~$ offlineimap  --info
OfflineIMAP 6.5.4
  Licensed under the GNU GPL v2+ (v2 or any later version)
Remote repository 'RemoteAccount': type 'IMAP'
Host: mail.example.org Port: 993 SSL: True
Establishing connection to mail.example.org:993
Server welcome string: * OK The Microsoft Exchange IMAP4 service is ready.
Server capabilities: ('IMAP4', 'IMAP4REV1', 'AUTH=PLAIN', 'UIDPLUS', 'CHILDREN', 'IDLE', 'NAMESPACE', 'LITERAL+')
 
Then a list of folders is appended which I ommit in this email.
 
This is the error I receive, then offline imap aborts.
 

OfflineIMAP 6.5.4
  Licensed under the GNU GPL v2+ (v2 or any later version)
Account sync Account:
 *** Processing account Account
 Establishing connection to mail.example.org:993
Folder Archives [acc: Account]:
 Syncing Archives: IMAP -> Maildir
Folder Archives/2011 [acc: Account]:
 Syncing Archives/2011: IMAP -> Maildir
 Copy message 1 (1 of 792) RemoteAccount:Archives/2011 -> LocalAccount
 Copy message 2 (2 of 792) RemoteAccount:Archives/2011 -> LocalAccount
 Copy message 3 (3 of 792) RemoteAccount:Archives/2011 -> LocalAccount
 Copy message 4 (4 of 792) RemoteAccount:Archives/2011 -> LocalAccount
 Copy message 5 (5 of 792) RemoteAccount:Archives/2011 -> LocalAccount
 Copy message 6 (6 of 792) RemoteAccount:Archives/2011 -> LocalAccount
 Copy message 7 (7 of 792) RemoteAccount:Archives/2011 -> LocalAccount
Copy message from RemoteAccount:Archives/2011:
 Establishing connection to mail.example.org:993
 ERROR: list.remove(x): x not in list
Folder Archives/2011 [acc: Account]:
 Copy message 8 (8 of 792) RemoteAccount:Archives/2011 -> LocalAccount
Thread 'Copy message from RemoteAccount:Archives/2011' terminated with exception:
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/offlineimap/threadutil.py", line 156, in run
    Thread.run(self)
  File "/usr/lib/python2.7/threading.py", line 763, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib/python2.7/dist-packages/offlineimap/folder/Base.py", line 330, in copymessageto
    message = self.getmessage(uid)
  File "/usr/lib/python2.7/dist-packages/offlineimap/folder/IMAP.py", line 253, in getmessage
    self.imapserver.releaseconnection(imapobj)
  File "/usr/lib/python2.7/dist-packages/offlineimap/imapserver.py", line 112, in releaseconnection
    self.assignedconnections.remove(connection)
ValueError: list.remove(x): x not in list
Last 1 debug messages logged for Copy message from RemoteAccount:Archives/2011 prior to exception:
thread: Register new thread 'Copy message from RemoteAccount:Archives/2011' (account 'Account')
ERROR: Exceptions occurred during the run!
ERROR: list.remove(x): x not in list
------------------------
I tried to google the error as it is quite common but I could not get a fix for it. What is causing this error and how can I solve this issue? At one point I could see my clear text password in the debug output like this
imap: Attempting PLAIN authentication
imap: __plainhandler: returning MY-USERNAME-AND-PASSWORD
 
The SSL config has never been diasabled. Is this an internal debugging message and or have my credentials have been transmitted in cleartext?
 
Thank you in advance,
please let me know if you need further information.
 
Regards
MightyApe