[CentOS] apache, krb5 annoyances

Something I've been fighting since yesterday... I got trac installed, and
working. Then I had to add security. Got all the moving pieces in -
mod_ssl, auth_kerb. If I go to https://hostname/trac, everything's fine, a
popup window asks for username and password. But if I go to
https://hostname.f.q.d.n/trac, it fails, returning a 500? 501? Internal
server error. I'm on a workstation running CentOS 6.5; my user, on Windows
and running IE, gets the same.

But if I open another firefox window with -P --no-remote, and pick another
profile, it works. I certainly have no idea what to try in IE.... But I
think there's some other misconfiguration of apache.

Anyone have any thoughts on the matter? I don't think management will
appreciate a head-shaped hole in the wall by my cube....

  mark