Currently, when in a Timeline, we allow the user to reposition the Playhead in the Timeline by clicking-and-dragging it left or right.
Moving the Playhead horizontally, requires a click-and-hold of the leftmouse in order to move it.

However, after resizing the Application Window to another size, the Playhead continues to capture the Mouse, as if LeftClick was still being actuated.

Video attached

Repro Steps:

1) Create a new Studio Project featuring a MainPage.xaml

2) Navigate to the Animation Panel, and create a new Storyboard. This will expose the Timeline.

3) Click-and-drag the Playhead left and right along the Timeline.
Observe how the Playhead moves when clicked-and-dragged as expected.

4) Resize the Studio application window to any other dimension.

5) Without clicking, hover the cursor over the Timeline Time Graph (the strip at the top that contains the ticks and numbers).
Observe how the Playhead moves left and right without clicking-and-dragging it.

Expected Results: Resizing the application window does not trigger a 'capture' of the Playhead, and the Playhead can only be moved by clicking-and-dragging it directly.