Every database you create while logged into a workgroup file will use that
workgroup file.
Think of it this way. Access is *always* using a workgroup file. By
default it uses System.MDW which doesn't have a password on the Admin user
so you don't get a login prompt. If you create 1000 MDB files while joined
to System.MDW then they are all using System.MDW as their Workgroup file.
If you did the same while joined to a "secure" workgroup file (MyWrkGrp.MDW
for example) the same would apply. Every file you created would then use
MyWrkGrp.MDW as its Workgroup file.