The value for UIKeyboardAnimationDurationUserInfoKey is zero when the QuickType panel is showing / hiding. What for?

I am using UIKeyboardWillChangeFrameNotification

to change my views when the keyboard is displayed.

To animate along with the keyboard, I use a user info dictionary NSNotification

to get the duration of the animation with a key UIKeyboardAnimationDurationUserInfoKey

.

This works when the keyboard is shown and hidden. But not when its frame changes, while it is already displayed, for example. when the QuickType panel is shown / hidden.

Does anyone know why this is so? And how should I solve this problem?