work-shared not being correctly shared

[Phil Blundell <philb@gnu.org>]

Since updating to the latest versions of bitbake and oe-core I'm
experiencing some sort of conflict to do with the gcc sources in
tmp/work-shared.

What seems to be happening is that all the different recipes which share
that source directory are using different stamp values for do_unpack.
So, for example, I can do:

$ bitbake -f -c unpack gcc-cross
[ source unpacks ]
$ ls -l tmp-eglibc/stamps/work-shared/gcc-4.7.2-r13.do_unpack*
-rw-rw-r-- 1 pb pb 0 2012-09-24 15:37
tmp-eglibc/stamps/work-shared/gcc-4.7.2-r13.do_unpack.ea6dd89ddae3dcc205848b41ce0251cd
$ bitbake -f -c unpack gcc-cross
[ nothing happens ]
$ bitbake -f -c unpack gcc-cross
[ still nothing happens ]
$ bitbake -f -c unpack gcc-runtime
[ source unpacks again ]
$ ls -l tmp-eglibc/stamps/work-shared/gcc-4.7.2-r13.do_unpack*
-rw-rw-r-- 1 pb pb 0 2012-09-24 15:42
tmp-eglibc/stamps/work-shared/gcc-4.7.2-r13.do_unpack.e677db6d46e8c0c6109b02302aa477d0
$ bitbake -f -c unpack gcc-runtime
[ nothing happens ]

Worse, if I set BB_NUMBER_THREADS to some high number, I seem to end up
with multiple competing tasks all trying to unpack in parallel and the
build never makes any real forward progress.

Does anybody have any insight into what is going wrong here and how I
should debug it?

thanks

p.