You're right, it is a network manager bug. But I (and you too) can get around it by running openvpn from the command line. You've probably done at least a few of these steps, but just in case (and for the benefit of others) I'll do a full step-by-step.

First install the required packages

sudo apt-get install network-manager network-manager-openvpn network-manager-openvpn-gnome

Create Files
These files must be kept safe and private at all times

1. Make a directory called openvpn in your home directory Copy your VPN
   client file (renamed client.ovpn) into directory openvpn


2. Optional: Keep an original copy of the file – call it client.ovpn.orig


3. Next we will create 4 files under the openvpn directory.


4. See the bottom of this file for how to automate the following steps


5. Open the client.ovpn file in a text editor.


6. Create a file called ca.crt – copy the text between <ca> and </ca> from client.ovpn into this file


7. Create a file called client.crt – copy the text between <cert> and
   </cert> from client.ovpn into this file


8. Create a file called client.key – copy the text between <key> and </key> from client.ovpn into this file


9. Create a file called ta.key – copy the text between
   <tls-auth> and </tls-auth> from client.ovpn into this file
   At this point I have a total of 6 files under my openvpn directory (including the backup file)

5-9 I've just worked out how to do bash script. Whoop Copy the following into a text file:

#!/bin/bash

sed '1,/<ca>/d;/</ca>/,$d' client.ovpn > ca.crt

sed '1,/<cert>/d;/</cert>/,$d' client.ovpn > client.crt

sed '1,/<key>/d;/</key>/,$d' client.ovpn > client.key

sed '1,/<tls-auth>/d;/</tls-auth>/,$d' client.ovpn > ta.key

I saved the file as openvpnconvert in the openvpn folder along with the client.ovpn file. Made it executable with the command chmod a+x:

chmod a+x openvpnconvert

And then ran it:

./openvpnconvert

Modify the client.ovpn file

Just before the ## —–BEGIN RSA SIGNATURE—– line add the below lines and save

ca ca.crt

cert client.crt

key client.key

tls-auth ta.key

Finally, you need to run openvpn from the Command Line Interface (CLI)

cd into the openvpn folder

cd openvpn

Run openvpn, if you're using the filenames I specified, see below, otherwise use your filenames.

sudo openvpn --client --config ~/openvpn/client.ovpn --ca ~/openvpn/ca.crt

I'm currently running OpenVPN, which I set up using exactly these steps. Hope it works equally well for others.

Sources:

Creating Files - http://naveensnayak.wordpress.com/2013/03/04/ubuntu-openvpn-with-ovpn-file/

Running from the Command Line - http://ubuntuforums.org/showthread.php?t=2206811