I have a menu-structure on the left of my page, like
Topic 1
- Subtopic A
- Subtopic B
- Subtopic C
Topic 2
- Subtopic 2A
- Subtopic 2B
etc.
I want to link to some of thoses nodes via the Primary Links, e.g. one Primary Link should go to Subtopic 2A. When I create the two menu entries, and open the node, my custom menu collapses instead of showing the tree for Topic 2.

How can I change this behaviour?