Got a comment on #kerberos IRC today:

10:13 <tobybl> Hello, does anyone know if the bug in 
               http://krbdev.mit.edu/rt/Ticket/Display.html?id=5890 is still 
               unfixed?  It seems the case to me, but the code has changed a 
               fair bit since it was reported.

It does look like it might still be a problem.  kadm5_get_admin_service_name() doesn't take a 
params input, so it can't see the overridden ADMIN_SERVER config.