QDeclarativeItem signal childrenChanged is never emitted

I'm trying to make a QML component that somehow takes care of its children. In order to do that I need to know when a new child is added and/or removed.
My initial idea was to implement the onChildrenChanged handler but the associate signal handler is never called.

Tested with the latest Qt/master branch as of today. Commit df6549d1b95af017305744af04a7bb3b10025660

To reproduce, run attached example and:

1) Click the black button, check the console output, children count is "1"
2) Click one of the coloured rectangles
3) Click the black button again, console output, children count is "2"

onChildrenChanged is not called in this process.