I am setting my tweenRotation.from dynamically when an event fires, then playing the tween. This worked in 2.6.3.
After updating to 2.6.4 I have to comment out the new Update() call on line 300 of UITweener.cs for it to work. Otherwise the tween goes immediately to the tweenRotation.to (or I'm doing something that I shouldn't have done before but worked) I don't actually see the tween check mark activate, but it does get to the end result.