Macbook doesn't display on external screen until after I log in (Yosemite). How to fix?

I have a macbook pro (mid-2011) and an HP Pavilion 22bw (prob inconsequential) connected via a Thunderbolt DVI Adapter.

Ever since installing Yosemite, I now need to open the macbook pro and log in via its own screen, rather than the external monitor. It simply does not display / send any signal to the external screen until AFTER I'm logged in.

Does anyone else have this issue? Is there any other option? This is highly inconvenient with how my workspace is set up.

Thanks!