network-manager loose VPN credentials

I am using network-manager-gnome for PPTP-VPN connection.
It worked fine for about a month and it was stable connected.
I am also using vpnautoconnect (source:barraudmanuel) which also works fine and has in my opinion nothing to do with this error.

Actually now it takes 1-5 days until the VPN-credentials (not the username, only the passphrase) are lost.
After that I can see in the GUI of networkmanager where to configure VPN the field passphrase is empty.
manually adding the passphrase again doesn't help.
restarting service network-manager doesn't help.
It only works again after rebooting.
I've noticed today that "flight mode" was activated maybe it has sthg. to do with it.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: network-manager-pptp-gnome 0.9.4.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.8.0-34.49~precise1-generic 3.8.13.12
Uname: Linux 3.8.0-34-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.6
Architecture: amd64
Date: Thu Jan 2 13:24:02 2014
InstallationMedia: Ubuntu 12.04.3 LTS "Precise Pangolin" - Release amd64 (20130820.1)
MarkForUpload: True
ProcEnviron:
 LANGUAGE=de_DE:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: network-manager-pptp
UpgradeStatus: No upgrade log present (probably fresh install)