When browsing with object relations which uses different default elements, the frame stays the same which means as the first one was (the first has the right behaviour and not the second).
We have the same problem with the back-office and the API process in an external module (eZContentBrowse::browse).
The problem seems to be linked with the design admin2 because this feature works well with standard admin design.

Steps to reproduce

• Create a class with two different kind of object relations
  The first relation (content relation) defines the default location to a content structure element (content top node).
  The second relation (user relation) defines the default location to a user group located in the user top node.
• Then, you try to create a content with this new class.
• First, assign a content to the content relation. As you can see, the tree and the frame is correctly rendered.
• Secondly, assign a user to the user relation.
  Here is the issue: the frame is the same as previously. The content structure menu and tabs seem to have been cached and still let appear the standard content information. The expected behavior would of course be to have a user menu and the "user" tab highlighted.
  Inverting the order of adding relations will just the first one to be used on both, then seems to be a cache-linked issue.