Mapping Command-Shift to Option-Shift Seems Impossible. Any help much appreciated!

Hi all. I'd like to set up BTT so that when I hit the trigger command-shift BTT changes it to the assigned action option-shift (I use it for selecting text and other items). I tried setting this up in the keyboard section but simply can't make it work. I can get the record a sequence to record command-shift (for some reason I can't enter it as a shortcut). But when I go to enter the "Trigger Other Keyboard Shortcut" and press Option-Shift, the cursor turns into a crosshairs and nothing shows up. I tried a workaround by pasting the symbols for Option-Shift into the "Trigger Other Keyboard Shortcut" box and they show up, but when I click away they end up being changed so that the "other keyboard shortcut" is simply "A." Very confused and frustrated. Any help much appreciated! I'm using version 2.428(788).