BUG #5253: installer fails to populate data directory

The following bug has been logged online:

Bug reference: 5253
Logged by: Daniel Convissor
Email address: danielc(at)analysisandsolutions(dot)com
PostgreSQL version: 8.4.2-1
Operating system: Windows XP Pro SP3
Description: installer fails to populate data directory
Details:

It seems Bug #4785 hasn't been resolved. I downloaded the one click
installer tonight and have hit a snag. Running
postgresql-8.4.2-1-windows.exe produces the following error:

vvvv
Problem running post-install step. Installation may not complete correctly.
Error reading the C:/Program Files/PostgreSQL/8.4/data/postgresql.conf
^^^^

Turns out the data directory is completely empty. During the install, I did
_not_ un-check the box asking if I wanted to "Install pl/pgsql in template1
database", so it should have been in there as well.

This is a standalone computer, not on a domain. I ran the installer while
logged into the Administrator account. Both I and the pre-existing
"postgres" user[1] have permissions to the directory.

cacls "C:\Program Files\PostgreSQL\8.4\data"

C:\Program Files\PostgreSQL\8.4\data DANT41\postgres:(OI)(CI)C
BUILTIN\Users:R
BUILTIN\Users:(OI)(CI)(IO)(special
access:)
GENERIC_READ

GENERIC_EXECUTE
BUILTIN\Power Users:C
BUILTIN\Power Users:(OI)(CI)(IO)C
BUILTIN\Administrators:F
BUILTIN\Administrators:(OI)(CI)(IO)F
NT AUTHORITY\SYSTEM:F
NT AUTHORITY\SYSTEM:(OI)(CI)(IO)F
DANT41\theadmin:F
CREATOR OWNER:(OI)(CI)(IO)F

NB: "theadmin" is the administrator user on this machine.

[1] I had Postgres 8.1 installed a while ago. Haven't used it in a while.
I uninstalled it before attempting to install 8.4.