Calling QDBusPendingReply::waitForFinished() on seperate objects from multiple threads causes crash.

Given a multi-threaded environment such that:

a) Multiple threads each create their own instance of a DBus proxy object
b) Those objects share the same underlying QDBusConnection object

Performing a blocking call, in multiple threads simultainiously, via means of QDBusPendingReply::waitForFinished(), eventually causes a crash within libdbus-1, producing the following error:

process 10929: arguments to dbus_pending_call_block() were incorrect, assertion "pending != NULL" failed in file dbus-pending-call.c line 704.

Backtrace:

#2 0x0000003a3c630035 in _dbus_abort () at dbus-sysdeps.c:94
#3 0x0000003a3c6270c5 in _dbus_warn_check_failed (format=
0x3a3c636290 "arguments to %s() were incorrect, assertion \"%s\" failed in file %s line %d.\nThis is normally a bug in some application using the D-Bus
library.\n") at dbus-internals.c:289
#4 0x000000397182144a in q_dbus_pending_call_block (pending=0x0)
at /home/thiago/src/qt/qt-4.8/src/dbus/qdbus_symbols_p.h:313
#5 QDBusConnectionPrivate::waitForFinished(QDBusPendingCallPrivate*)
(this=0x621220, pcall=0x7fffcc002fc0)
at /home/thiago/src/qt/qt-4.8/src/dbus/qdbusintegrator.cpp:1776

A reproducible test case is attached.