I don't remember if AS 6 added the ALLUSERS property in the Property Manager for you or not. My guess is that it did. Installing per machine is a function of both the ALLUSERS property *and* the current account privileges.
For example, the ALLUSERS property can be set to 1 and install per machine when the install is run with Admin privileges and install per user if simple user privileges are used.
In addition, if the ALLUSERS property is not specified, the install will always be per user.
Run the install with logging enabled and look for the current value of the ALLUSERS property in the log file.