Shift modifier key not working (how to disable Space Cadet?)

I would like to have a Shift secondary modifier on my space and backspace keys. It doesn’t seem to work. Using Command as modifier does seem to work, so something fishy is going on.

I read elesewhere here that the Spacecadet feature may be the culprit. It seems like I have it enabled. How do I disable it? The UI buttons “Enable” and “Space” doesn’t make sense to me (apart from the former). When I click “Space” the key definition says “Ctrl+TopsyTurvy+ Space” which doesn’t make much sense to me either.

(Atreus with firmware 0.91.1+74)

Update: This now works after upgrading my firmware. Hooray!