L4_ThreadSwitch behaviour

My question is related to both L4Ka::Pistachio and
NICTA::Pistachio-embedded, thus I'm mailing to both lists.

Consider the following test cases:

Case A
======
1. The root thread creates a new thread in a new address space (AS):
   L4_ThreadControl( ping_tid, ping_tid, master_tid, L4_nilthread,
                     L4_anythread, L4_anythread, NOUTCB )
   L4_SpaceControl( ping_tid, 0, kip_area, utcb_area, &control )
   L4_ThreadControl( ping_tid, ping_tid, master_tid, pager_tid,
                     L4_anythread, L4_anythread, UTCB(0) )
   L4_Start( ping_tid, (L4_Word_t)ping_stack + sizeof(ping_stack) - 32,
             START_ADDR(testing_thread) )

2. The root thread "refills" it's time slice (maybe that's bogus, but it
is meant to ensure a full time slice is donated): L4_Yield();

3. The root thread donates the rest of it's time slice to the new
thread:
   L4_ThreadSwitch( ping_tid );

Case B
======
1. The root thread creates a new thread in a new AS
2. The root thread waits for a startup IPC from the new thread (of
course, the new thread has to be altered to send such an IPC)
3. The root thread "refills" it's time slice
4. The root thread donates the rest of it's time slice to the new thread

Problem:
Case A won't work, but Case B does. For Case A the new thread won't run,
even though it's active and in the ready queue. The only difference is
that in Case B the pages which hold the code are already mapped in the
new threads AS.

I think this is a generic issue, however I'm working with a "homemade"
PowerPC Version of NICTA::Pistachio-embedded based on the Karlsruhe
version.

Questions:
1.) Why does Case A fail (or at least don't do anything)?
2.) Is there are difference between the semantics used in
L4Ka::Pistachio and NICTA::Pistachio-embedded (or between X2 and N1)?

Any opinions, experiences, fairy tales would be appreciated! :-)

Martin.