If you preview a form in Notes from the 8.5 designer client, and then go back to the designer client to alter a field, the programming pane no longer shows the selected field. You can navigate to it via the Objects view, but the only real workaround is to close the form and reopen it.
BTW, opening a form can take up to 30 seconds, without any user feedback (makingyou think that you have not double-clicked!)
Jim.