OmniGraffle Pro Insists on Saving .graffle as a Directory

OmniGraffle Pro Insists on Saving .graffle as a Directory:

>Always flat:
>defaults write com.omnigroup.OmniGraffle PrivateGraffleFlatFile 0
>
>Flat unless there are images (the normal behavior):
>defaults write com.omnigroup.OmniGraffle PrivateGraffleFlatFile 1
>
>Always as a package:
>defaults write com.omnigroup.OmniGraffle PrivateGraffleFlatFile 2

(Use "OmniGraffle" or "OmniGrafflePro" as appropriate.)