I set up an IPB and a Converge, and set the IPB as an application of the Converge.

The administrator's name and password of the IPB and Converge are the same.

Then I changed the IPB admin password, I was confused by the things below:

The Converge\index.php password changed automaticly.

The Converge\admin\index.php password not changed.

Why did the Converge\index.php password change but the Converge\admin\index.php password not change?

Thanks.

In Converge, your admin account is separate from your public account - to change the admin password you'd have to login to the admin area and change it under Manage Administrators.

It would be a good idea in the future to merge the two records, however, as there isn't a big need to keep them separate.

Yes, no need to keep them separate.