当 TransitioningContentControl 放在 TabControl 的初始选中的 TabItem 中时，它不会重新播放其过渡动画。

Describe the bug When the TransitioningContentControl is placed in the first TabItem (index 0) of the TabControl, the transition animation is not triggered when switching back from another tab. The animation of the TransitioningContentControl in non-first TabItem (index >= 1) works normally.