FontFamilyComboBox: Preview vs. UndoStack

Hello everybody,

we have noticed (in your SampleBrowser, too) that previewing a FontFamily from the FontFamilyComboBox (--> 'ValueCommandParameterAction.Preview') already adds to the UndoStack of a RichTextBox. Our expectations were, indeed, that this only happens in the 'ValueCommandParameterAction.Commit' case.

So, can you tell me how to achieve this?

Thanks in advance,

 Detlef Peters