when i unlock mine i usually just come to a complete stop and unlock them. i have never had a problem with them not unlocking. if you are going straight and none of the tires are spinning then you can unlock it too. even at speeds. i have never done this and dont ever plan on trying this, but supposedly you can.
as for the front i dont know whats up with that. sounds very weird. it definitely makes it harder to turn and wont turn as for but it have never not let me turn a direction and pull me in the opposite.
good luck man!
