Both of my screens are rotated so I haven't tried this but has anyone that doesn't have a rotated screen tried an NVRam reset (more widely known as PRAM)?
http://support.apple.com/kb/HT1379
I would unplug the adapter, reset the NVRam and then plug in the adapter.
Resetting NVRam usually clears resolution settings and I'm thinking its worth a shot.
To the DisplayLink Team: I'm still very disappointed that you cannot be bothered to update the Mac software page to exercise caution when updating due to some known issues. I think it is ridiculous that people would have to come to the forum and research this. My $.02