I don't immediately recognize anything wrong with the configuration you describe. Moreover, I note that whether "devforge" is a valid environment is completely irrelevant to whether another module should be able to achieve the intended effect by including "$confdir/environments/devforge/modules" in its own modulepath.
I'm inclined to suppose that something else is happening here. Did the ownership or permissions (or ACLs or SELinux labels) change on any of the directories or files you moved? Is it possibly something dumb, such as having moved stdlib into the wrong directory (e.g. $confdir/environments/devforge/modules/modules/stdlib), or having reverted to a version where they were never moved at all?
Details of the issue aside, have you considered putting modules that are intended to be shared across environments somewhere outside the environments/ subtree?
John