[Lazarus] OnUndock event question

[Vojtěch Čihák]

Hi,
 
when is triggered OnUndock event of the form?
 
I have Panel (UseDockManager=True, DockSite=True) and I dock there a form (it is a toolwin) with method Dock(Panel, rect);
Then I undock it with Dock(nil, rect); 
 
It seems that OnUndock is never triggered, I also tried OnUndock of the panel but it does not work either.
 
How should I do it right?
 
Thanks