Still more, Re: This is weird (cross-posted to Tomcat and Debian Lists): Tomcat 8.5 is going to /var/lib/tomcat7/webapps/ROOT
I also stuck a similar named trivial static context into
/var/lib/tomcat7/webapps (with a different directory name: "foobar" in
Tomcat 8, "bozbar" in Tomcat 7).
In theory, Tomcat 8.5 should be able to see the foobar context, but not
the bozbar context; this is also true in practice.
So it's something specific to the root context.
James H. H. Lampert