Scrollview's position jumps during animation when contentOffset has value

I'm using the TPKeyboardAvoidingScrollView found here: https://github.com/michaeltyson/TPKeyboardAvoiding

Here are the relevant code blocks from that class:

- (void)keyboardWillShow:(NSNotification*)notification {
if ( !CGRectEqualToRect(priorFrame, CGRectZero) ) return;

UIView *firstResponder = [self findFirstResponderBeneathView:self];
if ( !firstResponder ) {
    // No child view is the first responder - nothing to do here
    return;
}

priorFrame = self.frame;

// Use this view's coordinate system
CGRect keyboardBounds = [self convertRect:[[[notification userInfo] objectForKey:_UIKeyboardFrameEndUserInfoKey] CGRectValue] fromView:nil];
CGRect screenBounds = [self convertRect:[UIScreen mainScreen].bounds fromView:nil];
if ( keyboardBounds.origin.y == 0 ) keyboardBounds.origin = CGPointMake(0, screenBounds.size.height - keyboardBounds.size.height);
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CGFloat spaceAboveKeyboard = keyboardBounds.origin.y - self.bounds.origin.y;
CGFloat offset = -1;

CGRect newFrame = self.frame;
newFrame.size.height -= keyboardBounds.size.height - 
                            ((keyboardBounds.origin.y+keyboardBounds.size.height) 
                                - (self.bounds.origin.y+self.bounds.size.height));

CGRect firstResponderFrame = [firstResponder convertRect:firstResponder.bounds toView:self];
if ( firstResponderFrame.origin.y + firstResponderFrame.size.height >= screenBounds.origin.y + screenBounds.size.height - keyboardBounds.size.height ) {
    // Prepare to scroll to make sure the view is above the keyboard
    offset = firstResponderFrame.origin.y + self.contentOffset.y;
    if ( self.contentSize.height - offset < newFrame.size.height ) {
        // Scroll to the bottom
        offset = self.contentSize.height - newFrame.size.height;
    } else {
        if ( firstResponder.bounds.size.height < spaceAboveKeyboard ) {
            // Center vertically if there's room
            offset -= floor((spaceAboveKeyboard-firstResponder.bounds.size.height)/2.0);
        }
        if ( offset + newFrame.size.height > self.contentSize.height ) {
            // Clamp to content size
            offset = self.contentSize.height - newFrame.size.height;
        }
    }
}

// Shrink view's height by the keyboard's height, and scroll to show the text field/view being edited
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationCurve:[[[notification userInfo] objectForKey:UIKeyboardAnimationCurveUserInfoKey] intValue]];
[UIView setAnimationDuration:[[[notification userInfo] objectForKey:UIKeyboardAnimationDurationUserInfoKey] floatValue]];
self.frame = newFrame;

if ( offset != -1 ) {
    [self setContentOffset:CGPointMake(self.contentOffset.x, offset) animated:YES];
}
[UIView commitAnimations];
}

- (void)keyboardWillHide:(NSNotification*)notification {
if ( CGRectEqualToRect(priorFrame, CGRectZero) ) return;

// Restore dimensions to prior size
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationCurve:[[[notification userInfo] objectForKey:UIKeyboardAnimationCurveUserInfoKey] intValue]];
[UIView setAnimationDuration:[[[notification userInfo] objectForKey:UIKeyboardAnimationDurationUserInfoKey] floatValue]];
self.frame = priorFrame;
priorFrame = CGRectZero;
[UIView commitAnimations];
}

I'm having an issue that when the keyboard starts to hide, the scrollView immediately jumps up so it's origin is above the top of the window. It then animates into its proper position.

I've found out that this only happens when the contentOffset is anything > 0 when the animation runs.

While debugging I noticed the content offset was 54 when the keyboard dismiss animation begins. I found that if I added this code to the beginning of keyboardWillHide:

priorFrame.size.height -= self.contentOffset;

...then no jump would occur and the animation would run properly, but the scrollView would be too short in the end.

Any ideas?

Also note that the normal frame for my scrollView is (0, 44, 320, 416) because it is positioned below a title bar.

It seems like this might be a bug in UIKit, unsure. I found a fix by animating contentInset instead of the frame.size.height. You can see it in my fork of the project http://github.com/wordofchristian/TPKeyboardAvoiding