Keyboard dismiss when focus on textfield

When I put a textfield as a child if page_flip_builder, the keyboard automatically dismiss every time I focus on it. Meanwhile, the keyboard work fine when I remove the Key of page_flip_builder (however, I cannot control flipping action). I am not sure if AnimationController has some conflicts with the Textfield. See anyone has some idea about it.

The following is my sample code
> PageFlipBuilder(
key: pageFlipKey,
frontBuilder: (_) => Container(
child: TextField(),
),
backBuilder: (_) => Container(
child: TextField(),
),
flipAxis: Axis.horizontal,
maxTilt: 0.003,
maxScale: 0.2,
onFlipComplete: (isFrontSide) => print('isFrontSide: $isFrontSide'),
);

Start by reproducing the sample with a keyed PageFlipBuilder containing TextFields on both sides, then compare it with the same widget without the key. Investigate the PageFlipBuilder focus and animation behavior; done means the keyboard stays open when a TextField receives focus while the key still allows flipping control.

Written by the indexing model from the issue text.