Automatic config.php writing not working well

Hi

I´ve experienced the problem twice,

once on local using wamp-server , and once on mi server.

When you try to use the automatic config.php option, it does not write the db conection data. the only think it wrote was the server-url.

it did´nt write : db username, db-name nore db-password.

I´ve checked the ChMod settings on the files, and everything seemed to be well.

Did someone else experience this problem.
Need to know, before I post it as a bug