Dock widget allowed areas in QMainWindow

hi Everyone (anbd sorry for my bad english :) ),

Here is my problem:

My MainWindow (allow nested, allow tabbed) have 3 DockWidgets created with qtcreator's designer. The first one that can only be floating or docked on the left, another one which can only be floating or docked on the bottom, and the third can only be dock on top or right and not floating.
The problem is that at runtime I add some dock widgets in my main window and tab them with the third dock widget, which works great, but even if I set its allowed areas not to dock on left or bottom, i can “tab” them to the left and bottom with the two others created with the designer.

Where is the catch ?

Thanks for the replies :)