Found the problem: This is the only parameter in lowercase (orientation), but documentation states it uppercase.
getDevelopSettings()['orientation'] results in 'AB', 'BC', 'CD', 'DA'
(Note: the crop settings (CropTop, etc) always assume orientation 'AB', thus the orientation has to be taken into account for manipulating the crop settings!)
I sill consider this a bug and should be fixed... although it will break scripts then... well at least the documentation should be corrected.