Windows re-installation problem

I uninstalled PostgreSQL from windows for the sake of re-installing (for
the sake of documenting an install for our product on a clean machine),
and now during re-install on the Service Configuration screen I get
"Invalid username specified: Logon failure: unknown user name or bad
password."

Fine makes sense, I was using a new password for the postgres user... so
I went to my computer management and deleted the postgres user, then
rebooted, came back to install... but the message is still there. Yes I
can rename the user from postgres to postgres2 or some such and things
work fine, but this isn't acceptable for me right now.

Anyone know what else may need to be purged from the system to allow a
re-install with the same name/new password? And what do the installer
developers think about possibly building that into the installer?