Open Radar

 
Summary:
When using a re-using UIViewPropertyAnimator that has previously started its animations, been reversed, and the completed them with a non-zero durationFactor (passed to `continueAnimation(withTimingParameters:durationFactor:)`), any subsequent animations you run with the same UIViewPropertyAnimator are performed much more slowly than the duration of the animator.

Steps to Reproduce:
1. Open the sample project and run it on iOS 10 or 11

Or:

1. Create a UIViewPropertyAnimator and hold on to it
2. Add some animations to it
3. Start and immediately pause the animator
4. Set isReversed = true
5. Call continue with a non-zero durationFactor
6. Re-use the animator for another set of animations

Expected Results:
The first animation occurs, then completes, then the second animation should be performed at the correct duration of 0.33 seconds

Actual Results:
After the first animation completes, the second animation takes over 1 second to complete

Version:
iOS 11

Notes:
- This is also a bug on iOS 10
- You can workaround this by re-creating UIViewPropertyAnimator instances for each set of animations
- This happens with linear curves and springs
- Passing 0 as the durationFactor fixes this issue, unless you want to impact the duration of the continuation
- See the attached sample project and video for the example