[Lazarus] Purpose of TControl.UpdateRolesForForm?

[Hans-Peter Diettrich]

This method is called by a form, when its Default or Cancel control 
changes. But why do the affected controls receive no hint about their 
new role?

What's the intended purpose of this method?

If it is used (overridden) only in TCustomButton, the (there) 
interesting information could be passed in added arguments.

TControl.ActiveDefaultControlChanged is much more informative, but I 
suspect an bug in the TCustomForm implementation - NewControl is always Nil.

Can somebody explain, or simplify the current mess in the LCL?

DoDi