I have almost the same problem; My pinky finger is just too darn resitant to do what I want it to do. The pinky on my bow hand keeps going staight when it's supposed to be curved. It's a little better when I'm really focused on it, but the moment my mind wanders it's back to the way it was.
And the pinky on my left hand has started giving me trouble with paly ing four on the 3rd(D) string and open on the 2nd(A) string. Oh, well. Practice, Practice, Practice (or Play, Play, Play).
Wow! my post was six
sentences! An all time record.