Two Front-ends, common back-end.

I am trying to set up an environment where two seperate and differently themes instances of wordpress are looking to a common database for content, that is, I want to have two different themes showing the same content.

I have the two instances running in my www and www/dev, showing the same content, as desired, but if I change the theme in either instance, that change is mirrored on the other. I assume this is because the theme is defined somewhere in the database.