The issue was caused by id_copy_no_main() changing pointers of constraints used
in pose to a newly allocated ID. This is correct, but caused confusion too our
copy on write remapping, because we are mimicing inplace duplication by copying
memory over from a temporarily duplicated ID to a proper placeholder. This was
causing dangling pointers in pose to a temporarily allocated ID.
Now we add special code to remapping callback which replaces temporary ID with
a proper one.
3212e72cfe