z-order and parenting

Hi,

Dunno if it is a feature or a bug, but something weird happens here (1.19pr3, html5)

layer container1 zorder=1
layer container2 zorder=5
layer button zorder=10 parent=container1

So, container2 is on top of container1, and my button, parented to container1 should be on top of both containers. It isn't ! container2 is on top of my button and my button doesn't capture mouse.

if I parent my button to container2 it works, but placement and some actions need button parented to container1

Is this a normal behavior ? Shouldn't all z-order be treated globally, independently of their parenting ?

Yes this is what I concluded experimenting it.
But wouldn't be possible to put z-order globally ? In html, you can mix divs and img z-index ...