As far as I understood the problem,
ObjectChoiceField internally adjusts
Label to the left and
Field with 'choices' to the right.
Plus Label allocates half of the width of the whole
ObjectChoiceField, the other half is for Choices.
So even if the Label is set to
null Choices will appear on the right side of the screen.
The other problem related to this issue is that the width of
ObjectChoiceField is set to max value, for example 320.
That is why one has to override
layout(int, int) and
paint(Graphics).
RIM UI Gurus correct me if I am wrong