Thanks for your reply.

That's the sort of property I was hoping for, but the UltraCurrencyEditor has neither "NullText" nor a "NullTextLabel" property. I also do not see anything exposing or accepting a DataFilter on the editor. It appears I would have to cast the UltraCurrencyEditor to an EmbeddableEditorBase to get any access to a DataFilter, but the CurrencyEditor does not implement EmbeddableEditorBase. Are there any other alternatives?

This code you have here will not do anything at all, because you are never setting conversionArgs.Handled to true. 

Is the EditorToDisplay conversion ever being called? It's possible that you are right and that the reason for this is that the masked editors never call this conversion. 

 I think you've nailed it on the head. I changed my code to....

        public object Convert( EditorDataFilterConvertArgs conversionArgs )
        {
            if( conversionArgs.Direction == ConversionDirection.EditorToDisplay )
            {
                conversionArgs.Handled = true;
                return conversionArgs.Value ?? NullText;
            }
            return conversionArgs.Value;
        }

Then debugged through this and never entered the if statement. The flow appears to go DisplayToEditor, then EditorToOwner, and finally OwnerToEditor. The EditorToDisplay never gets executed. Thanks again for all of your time and help, I'll begin researching other work-arounds.

I guess the EditorToDisplay conversion isn't allowed because you might pass back some text that doesn't fit the mask and the control would not be able to handle that. 

In that case, I would recommend a DrawFilter. That way you can draw the text yourself and you have total control over it.

In the helpfiles in the 'about' page of the WinCurrencyEditor is stated that it should support a Null Text - Is this now the case? and if so, from which version and how to use...

I'm not sure exactly what 'about' page you are referring to. But there is no NullText property on the UltraCurrencyEditor.