Bug#103289: Postinst error in debian-policy

["Graeme Merrall" <graeme@inetix.com.au>]

Package: debian-policy
Version: 3.1.1.1

When attempting a dist-upgrade from stable->testing->unstable installation
of debian-policy_3.5.5.0_all fails with the following message:
dpkg: error processing
/var/cache/apt/archives/debian-policy_3.5.5..0_all.deb (--unpack):
unable to install (supposed) new file into
'var/lib/dpkg/tmp.ci/postinst':Operation not permitted
Errors encounterd while processing:
/var/cache/apt/archives/debian-policy_3.5.5..0_all.deb

Running 'apt-get remove debian-policy' is more telling
dpkg: error processing debian-policy (--remove):
unable to delete /var/lib/dpkg/info/debian-policy.postinst':Operation not
permitted.

For some reason the perms on debian-policy.postinst are:
br-xr-S--t
and I cannot find a way to remove a block file.

I am using Debian GNU/Linux testing/unstable kernel 2.2.17-i386