An old problem, but either is re-appearing or wasn't fixed.
My 5 year old daughter loves to play, and her latest love is the tamed dog.
Her greatest frustration, however, is that her pet dog will not un-sit.
She's tried right-clicking with hand, bone, beef, hitting it, pouring water on it.
This is in creative mode. The dog tends to be in a tight area (blocks or chests, etc. around it except for a couple sides. She pushes the dog to move it around. It barks and shows love just fine, and exiting and re-loading does not fix it.
Recommended fix: as this is a recurring problem, and could either be in the use-item code or dog logic, I would recommend changing the dog right-click logic to have an option button like on the pocket edition. Further, because this is a child's delight, I would recommend extending this button to provide more behavior's. Sit, stay, guard, follow, play, hunt, etc.
Does this still happen on version 1.8.8? Were you logged out at the time of taming the dog/trying to make the dog unsit?