I'm afraid I don't have a specific answer to this issue, but I do know that the new controls in 1.2 are rather buggy - so it doesn't surprise me that you are seeing problems such as this.
If you haven't already done so, I'd encourage you to raise a defect under the 'runtime' section on the Javafx JIRA site at: http://javafx-jira.kenai.com/
Matthew Hegarty
2009-08-11 09:52:47