Dragged Item is Lost When Timeline Resizes Vertically

[hfi580]

See JS Bin for implementation.

A dragged timeline item no longer follows the mouse cursor when the timeline's height shrinks due to that drag. A user has to find the dragged item again afterwards.

This only happens when the timeline is short and vertically scrollable. The effect is greater when timeline items are tall, and the dragged item is near the bottom.