Nicolas,
thank You for fix, I've just did some testing on it and found some contents where assymetry still persists. cursor position is marked with <C-N-> and IT IS NOT PART OF FILE CONTENTS.
* head1
body1<C-1->
* head2
body2<C-3->
* head3.
body3
calling `org-forward-sentence' from <C-1-> will go to <C-3->, while IMO it should not go that far, I mean it should stop somewhere BEFORE body2 line and AFTER head2 line. This is where cursor is stopped when You travel from <C-3-> using `org-backward-sentence'.
regards.