Backdrops from previous themes won't clear (Sansa e2xx and Fuze)

[Hipshot]

Hi all:

I am trying to create separate .cfg files which among other things, load separate themes.  For example, "Day.cfg" sets high brightness, 60 seconds before display blanks, and a high contrast theme with album art.  "Day2.cfg" is the same except it selects a text-heavy field with no art. "Night.cfg" sets low brightness, 5 seconds before blanking, and a low contrast, minimalist theme.

The problem I am having is when I switch from "theme A" with a custom backdrop to "theme B" without one, theme A's backdrop remains in place underneath theme B's elements. 

I've tried setting the config which calls theme "B" to 'backdrop:     "  with no entry.  And I've tried creating an all black backdrop bmp and associating that with theme B in its config file.   

I can get the backdrop to go away from behind the WPS screen.  But I can't get it out from behind the menus unless I (every time) manually drill down to select "clear backdrop".

Am I missing something?  Is there something I can place in a .cfg file to completely clear all backdrops, or am I stuck with this??