From the Apple support pages:
»support.apple.com/kb/HT5219?view ··· en_US#12
"19. How do I connect my Mini DisplayPort monitor or monitor using a Mini DisplayPort adapter to my Thunderbolt-equipped Mac when I have other Thunderbolt devices connected?
When connecting a Mini DisplayPort display or a display using a Mini DisplayPort adapter to a Thunderbolt peripheral (except as described in question 14), make sure the display is connected at the end of the Thunderbolt chain. You can use only one Mini DisplayPort device in the Thunderbolt chain."