Diagram: Fixed collapsing/expanding nested subdiagrams
Diagram: Fixed collapsing/expanding nested subdiagrams

After collapsing and expanding a subdiagram, that contains other
subdiagrams, only the top level subdiagram reappeard.

mbeddr/mbeddr.core,mbeddr/mbeddr.core,mbeddr/mbeddr.core,mbeddr/mbeddr.core,mbeddr/mbeddr.core