[Lazarus] DockManager: how to truly close form

[Valdas Jankūnas]

Hello,

I decided to use DockManager in my project. I fount that closing 
secondary form by pressing a X button in window of that form it becomes 
hidden not destroyed.
  How to actually close (destroy and free) a secondary from when 
DockManager is used?
  "CloseAction:= caFree" not helped. I tried forcibly "Free" but that 
produces crash of app.

ps: sorry for bad English.

-- 
   Valdas Jankūnas