Question yet another menu problem :)

Only by a loose definition of modules. It is not listed under modules in the backend and the code is not in the joomla modules directory. As I said, it's coded directly into the template. splitmenu is the name given by joomlart to their php *template* file and parameter selection. It cannot be enabled/disabled, published elsewhere on the page, etc etc

As for my issue, no I wouldn't consider it a bug per se, it's a problem caused by a significant new "feature" in the way kunena handles it's internal menus in 1.6, taking the itemid not from the actual itemid chosen by the site desinger, but a separate itemid selected and created by kunena.

still hacking away at a mod_rewrite solution. No luck yet

got it, minor typo

This will allow you to fix the issue:

docs.kunena.com/index.php/Creating_customized_menus

You just need to learn how to use the new feature. Kunena doesn't pick up Itemid from the Kunena Menu if you create your own menu. Or you could use alias instead of having real item in main menu.

Once you will learn how to use the feature, it's actually very powerful. We just need to document all the missing details and use cases.