qemu-1.5.0 savevm error -95 while writing vm with ceph-rbd as storage-backend

With a running VM I encounter this strange behaviour, former qemu-versions don't show up such an error.
Perhaps this comes from the rbd-backend in qemu-1.5.0 in combination with ceph-0.56.6?

( -95 might be a general "Operation not supported" error? )

Up to 1.4.2 everything is OK with savevm, though.

Any help welcome, 

Oliver.