Hi,

This could happen if what you consider a child node is connected to parent node through link in opposite direction than one indicated by Diagram.ExpandOnIncoming property.

Collapse recursion will also stop if the currently processed node already has its expanded field set to false. E.g. this will happen if you add links and child nodes to a parent node that's currently collapsed (showing + sign), and try to collapse it again through ancestor node. To fix that, you could either call expand() on the node when adding children or directly set its expanded field to true, so collapse() method does not stop. Collapse method checks that field to prevent infinite recursion, so be careful if your diagram contains cycles.

I hope that helps,
Stoyan