I finally figured out what I had to do to make Apache 2.4 happy...
1) Unlike everything else in Apache, <Location> blocks are LAST-match-wins, not first. 2) If you have ProxyPass xxx configured in, say, <Location /> and then have <Location /server-status>, you must add a "ProxyPass !" directive in every more-specific location.
This is because all Location blocks get *merged* at parse-time into a single config data structure, apparently.
So by re-ordering <location> blocks and adding "ProxyPass !" to the namespace bits I didn't want to proxy, it works.
-Adam