Setup DMX Addressing tab Changes Model erratically

[stepdown34]

Hi,
When building my light fixtures in setup mode things run smoothly for a while. Declared fixtures show up properly on the editor. But every time I try to add a simple par can as a fixture and then assign it on the DMX tab, the "Model names" section of every other fixture already established will change to "par can" or become blank... which then screws up everything I have entered both in setup and editor. When I try to re-edit, it won't let me change the model name. I have to delete it completely and start over. But this has happened many times in a row and I can't get the entire light show entered before it randomly changes something. Anyone else experience this? Anyone Please help asap!!
Thanks
Mike

Running showxpress version 6.20 on a brand new macbook pro (intel) with snow leopard 10.6.3

[support]

You can send us your light show, and tell us what action to do to see the problem.
We will check that.

[support]

No feedback from stepdown34