I am seeing a behavior with 1.9.0 that I believe is a bug.
Setup:
Two puppet environments defined. (dev and factory)
Single domain defined. (domain.com)
Multiple subnets defined all belonging to the domain above.

Create a new host, select one of the puppet environments. Go to Interfaces and select edit. Attempt to set the Domain. There is no drop down. Cancel the edit interfaces dialog screen. Re-Edit and the drop down for the domain will work just fine. Also if you do not select a puppet environment initially, you can go to the edit dialog and select a domain. The issue seems to be related to selecting a puppet environment and then attempting to edit the interface. A quick cancel and re-edit resolves the issue.

I have tried this under chrome and IE with the same results