The anomaly seems to be that clicking on those buttons and making changes doesn't 'take', but deleting that menu and adding another using CSSMenuWriter (the installed extension) then I can go back at any time to edit!
I'm actually fine about this - don't need anything done - just thought it was odd!
Edit: Eric - have tried it again - and it worked fine. I have no idea what I did differently this time, but it must definitely have been human error (mine). Apologies for wasting time.