The Posture is a convenience classification to categorize keyposes into mechanically similar groups. For example: Pinch, OK, and C keyposes are considered pinch postures whereas Thumb and Fist are considered grasp postures. This type of high level classification will be more useful as we expand the number of supported keyposes and will enable developers to bypass evaluation of a specific keypose and instead query the posture in the event they only care about the base posture (e.g. when the hand is pinching vs a specific type of pinching).In this case, you would likely resolve most of the issues by querying the keypose instead of the posture from the gesture data.I'll address each of your listed issues in parenthesis.
Gesture=Fist: is returns "grasp" (valid: the Fist keypose is a Grasp posture)
Gesture=Ok: returns "pinch" it never thinks is "Ok" (valid: the Ok keypose is a Pinch posture)
Gesture=Thumbs: returns "grasp"... (valid: the thumb keypose is a Grasp posture)