"Open" button in File -> Open dialog box has identity issues

It doesn't know whether it wants to be a Button control type or a Pane control type (this is in Vista, by the way).

If I open UISpy, then open an Open File dialog, the "open" button is reported to be a Pane.
If I open an Open File dialog, then open UISpy, the "open" button is reported to be a Button.

It gets weirder.

If I let my program, which uses UIAutomation, find all the buttons in the open file dialog it reports the "open" button to be a Pane.
If I halt my program and step through in the debugger, it takes exactly the same path through the code, but reports the "open" button to be a button.

I'm pretty stuck on this - has anyone had a similar experience?