MMF 2 - Edit Mask Object Tabbing Error

I had three edit objects. I set the tabbing to be 51, 52, 53. I ran the program and everything tabbed fine.

Then I saw I needed to use the Mask Edit object instead to control data entry. I set the tabbing order of the objects to 51, 52, 53. In other words edit object, mask edit object, edit object.

Ran the program and found the tab would not jump from 51 to 52. Instead it jumped over the masked edit object and went from 51 to 53.

Is this an error with the mask edit object???? You should be able to tab to it.