Thanks, Jason, but sorry, maybe I wasn't completely clear. The trouble is I'm getting no 'sub-menu' tabs from the 'sub-menu' tab. (Is that 'level-3'?)
I've attached a screen cap of what the preview window shows. This is what I'm expecting — flyouts tabs on the primary dropdown. But all I'm getting in the output is the same as your test: just one primary dropdown, and no tabs shooting out from them.
FWIW, this seems to work OK on other menu themes, just not the one I'm trying to create.
Thanks again for your help!