Thanks Eric,
I mean when I create a site with Site Assist. SA uses its integrated menu-writer functionality to create the menu. If I create a site, then clicking the javascript icon by the SiteAssist-created menu invokes the CSSMenuWriter buttons in the properties panel.
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.