I'm using Finale 2010.r4

I have a measure with two layers and two double-flatted notes that coincide. I only want to show one set of double flats. I tried following the user-manual directions for hiding the accidental, but it doesn't seem to work. The instruction is to select the note in simply entry mode (with carrot or by ctrl clicking on note. Then typing the command Ctrl Shift hyphen. 

Does anyone know how to fix this?