the native and normal behavior is that your form maximize its window.
if your form.showWindow=2 (top level form) form.desktop have no consequence at all.
if you set at design time or at runtime (even in form.init,activate or other):
form.windowstate=2 your form mandatory maximize.

i tested many properties and they replicate the native behavior without problem.
conclusion:You have a code somewhere that prevents that.

shipping entier code is preferable to diagnostic.

ex: in form.moved event if you put: thisform.windowstate=0, the form dont stay maximized (it maximize and stay at windowstate=0 instantaneously with a flicker).

-NB: is your have some corruption?? rebuild it and try!