The original bug report is filed at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=411778

Summary:

Tracker causes dbus-python to segfault (or more precisely my
dbus-inspector application; but I shouldn't be able to do this with pure
python code). I'll clone the bug report to python-dbus, too. But it
should probably be fixed on both sides:

---
Introspect error: Connection was disconnected before a reply was
received
Introspection failed for org.freedesktop.Tracker (:1.956),
/org/freedesktop/DBus/Local
process 4277: arguments to dbus_pending_call_set_notify() were
incorrect, assertion "pending != NULL" failed in file
dbus-pending-call.c line 598.
This is normally a bug in some application using the D-Bus library.
[1]    4277 segmentation fault  ./dbus-inspector
---

It seems that trackerd disconnects when I'm trying to do introspection,
which apparently requires me to reinitialise dbus on the client side.
(other introspection errors on e.g. NetworkManager or Hal are handled
gracefully.)