postgresql upgrade: cannot start postmaster

[debian-throwaway1@pjt33.f2g.net]

I upgraded postgresql from 7.2.1-2woody5 to 7.2.1-2woody6 with apt-get, but
experienced some problems getting things working. I've put a redacted log of
what I did to fix it at http://pjt33.f2g.net/postgresql_upgrade_log.html - the
summary is that after running
    apt-get upgrade
I had to manually kill the existing postmaster and remove a lock-file, before
running apt-get again to get the configuration to complete.

I seem to recall having a similar problem the last time I upgraded postgresql,
but I can't find any discussion of this problem on the web. Is it unique to my
setup, or is it a known bug?

-----
Peter Taylor