Unhelpful initdb error message

Hi all,

After building Postgres and trying an initdb, I'm getting the following:

thom(at)swift:~/Development$ initdb
The files belonging to this database system will be owned by user "thom".
This user must also own the server process.

The database cluster will be initialized with locale en_GB.UTF-8.
The default database encoding has accordingly been set to UTF8.
The default text search configuration will be set to "english".

fixing permissions on existing directory /home/thom/Development/data ... ok
creating subdirectories ... ok
selecting default max_connections ... 10
selecting default shared_buffers ... 400kB
creating configuration files ... ok
creating template1 database in /home/thom/Development/data/base/1 ...
FATAL: could not remove old lock file "postmaster.pid": No such file
or directory
HINT: The file seems accidentally left over, but it could not be
removed. Please remove the file by hand and try again.
child process exited with exit code 1
initdb: removing contents of data directory "/home/thom/Development/data"

It can't remove an old lock file due to it not existing, but the hint
says it was left over but couldn't be removed. The hint contradicts
the error message. There is nothing in the data directory at all
before trying this, and nothing after. Repeating initdb yields the
same result.

But, if I rename the data directory to something else and mkdir data
again, all is well. I can make it break again by removing the new
data directory and renaming the old one back to data, still completely
empty. Note that throughout all of this, Postgres is running, but as
a separate user and using completely separate directories, since it's
the standard packaged version on Debian.

Can anyone suggest what is wrong here?

--
Thom