Thunderbolt displays will not receive input from Mini DisplayPort. Though the ports are physically identical, the display will only be driven by a Thunderbolt port.
The reverse, however, is possible. A Thunderbolt port will happily send input through a mini DP monitor.
For clarity:
- Thunderbolt Video Output -> MiniDP Monitor | Good!
- MiniDP Output -> Thunderbolt Monitor | Will not work!
You can read about it here (sorry about CNET) http://www.cnet.com/news/confusing-mini-displayport-with-thunderbolt/