"Show thumbnail preview" set to nothing doesn't stick

After setting "Show thumbnail preview" to nothing the thumbnail preview does indeed disappear, even after a restart, but the preview eventually reappears. If I go into the setting and change it and then change it back to nothing, the preview disappears again, but ultimately reappears. Is there any way to get the "nothing" setting to stick permanently. I do not have 7+TT set to run on startup. Thanks.