Thank you. Yes, I had forgotten to mention that neither have .htaccess (not necessary if you have access to the /settings/sites-available files, I thought).
I had tried:
RewriteRule content/treemenu/?$ /index_treemenu.php [L] in the apache2 sites-available entry on the testing server to with no effect (either dynamic disabled or enabled, clearing caches with --clear-all --purge each time).
I had also tried adding the .htaccess_root to the testing installation, both with and without dynamic enabled, clearing caches fully both ways--again, it didn't help.
<i>Thank you. Yes, I had forgotten to mention that neither have .htaccess (not necessary if you have access to the /settings/sites-available files, I thought).</i> That's true, but then you can still forget about .htaccess files messing things up, for example. Still, that was my only thought.
<i>But clearing the cache from the admin interface after republishing the root node did fix it.</i> Interesting. It's good to know that this could be a potential solution to similar problems.... weird though... Please share if you discover more.