postgresql install failure on Ubuntu 10.10

Hi,

I tried to install postgresql-8.4 from sources on a custom Ubuntu 10.10 liveCD.
I get an error during the installation process:
[...]
Configuring postgresql.conf to use port 5432...
update-alternatives: using /usr/share/postgresql/8.4/man/man1/postmaster.1.gz to

provide /usr/share/man/man1/postmaster.1.gz (postmaster.1.gz) in auto mode.
* Starting PostgreSQL 8.4 database server
* The PostgreSQL server failed to start. Please check the log output. [fail]

and the log shows:
2010-10-25 08:45:56 UTC LOG: database system was shut down at 2010-10-25
08:45:55 UTC
2010-10-25 08:45:56 UTC PANIC: could not open file
"pg_xlog/000000010000000000000000" (log file 0, segment 0): Invalid argument
2010-10-25 08:45:56 UTC LOG: incomplete startup packet

This bug has been reported by someone else (in spanish):
https://bugs.launchpad.net/ubuntu/+source/postgresql-8.4/+bug/658857

However, this install works perfectly once Ubuntu is installed.
Why is there a difference between install and live (try)?
Thank you very much for your help,

Vincent