If we chose to use the same account as for installation, the installer throws notice:
Notice: Undefined variable: exists in D:\Projects\MediaWiki branches\1.17\includes\installer\PostgresInstaller.php on line 299
and then refuses to continue with the following message:
The specified user "postgres" does not exist. Please click the "create account" checkbox below if you want to create it.
Apparently, some recent fixes weren't backported.
Version: 1.17.x
Severity: blocker