I am running Trac 0.11 on Centos 5.2.
I installed AccountManagerPlugin and configured an HtDigestStore module using the file trac.htdigest. Got everything working. Playing with chaining stores together (eventual goal is HtDigest + LDAP), I enabled the HtPasswdStore and then visited /trac/admin/accounts/config to configure. I set priority of HtDigestStore to 1 and priority of HtPasswdStore to 2 and set the file for HtPasswdStore to trac.htpasswd.
Clicked on save.
Visited the filename field for HtDigestStore and it had changed from trac.htdigest to trac.htpasswd.
Now it maybe that these two modules cannot be chained. For instance, the ini file only specifies ONE password_file, not two.
If the two cannot be changed, somehow that should be indicated to the user.