Multiple user groups - no overriding of permissions

[Tettinntil]

The vBulletin manual states:

Users in vBulletin may also belong to multiple usergroups. This is one method of creating exceptions to your permission scheme.

For example, you may have a user who belongs to group X, but needs to have access to the few extra options (such as attaching files to posts) given by group Y. You can make X this user?s primary group and make Y a secondary group.

The basic idea here is that if a user is in multiple groups and they specify conflicting permissions, the greater permission overrides. Thus, a yes will always override a no and a larger number will override a smaller number.

We have a user group that "does not accept" that other groups override the access. Users that have this group as their primary user group do not get other permissions (i.e. to other sub forums etc.) that their secondary user groups should allow them.

Does anyone know what can be the reason for this?