ValueChangeEvent not working on a tree root node - Vaadin 7.7.17

Vaadin 6 / 7 / 8 Framework UI
1

In my application I’ve a tree, the tree is selectable and immediate.
I’ve a change listener on the tree.
On every node the change listener fires normally, but on the root node it doesn’t fire at all.
Is it a bug ?
How can I solve ?
Tks