Currently we have a PowerConnect 6248 running version 2.2.0.3 firmware.  We have successfully configured Double VLANning and it is working great.  

However, occaisionally when we SSH to the device, it reboots itself, bringing down our MAN.  Documentation that we have found seems to indicate that issues like this are known to exist in this firmware version.  That being said, we decided to upgrade it to 3.2.0.10 (latest currently).  

After performing the upgrade, we found that we were unable to successfully perform QinQ tagging.  A before/after config diff shows that nothing appears to have changed, except for a few defaults and some syntax.  I've found a few posts where people have experienced VLAN and Double VLAN issues related to a similar firmware upgrade, but the posts did not lead me to understand what the issue was.  

Please find attached a copy of the config before and after.