BUG #2433: Using pg_dump in a .bat : Cannot avoid asking for user Name and Password

The following bug has been logged online:

Bug reference: 2433
Logged by: Jacques Gollion
Email address: jgollion(at)sambatechnologies(dot)com
PostgreSQL version: 8.1.3
Operating system: Windows 2000 SP4 Fr
Description: Using pg_dump in a .bat : Cannot avoid asking for user
Name and Password
Details:

I am trying to automatically save my database every day using the scheduled
Tasks manager.
I put pg_dump command in a .bat file containing the following line :
C:\postgres\bin\pg_dump -U im -h localhost -Z 0 -u -v -F c -f
F:/backup/dump/backup110506__ano pdb2000

The windows user name is im. There is a database role that is im. In the
directory C:\Documents and Settings\im\Application Data\postgresql there is
a file named pgpass.conf containing the following lines :
localhost:*:*:im:imhe
localhost:5432:*:postgres:imhe

I have checked with sysint/filemon.exe that the file pgpass.conf is read.

In fact I have just to type 'Enter' twice to start dump.

I do not understand what is wrong in my system to avoid typing anything.

Thank you in advance for your help.