forceFallback & scaled container produce continuously multiplied scale #1699

Problem:

When a container element wrapping the SortableJS interaction is being scaled with a CSS transform and forceFallback: true is being used, there appears to be an error in the calculation of scaling for the .sortable-fallback element, causing it to continually rescale ever smaller/larger on each drag position update.

With a scale of less than 1 on the ancestor element, the dragged item vanishes to oblivion and over-corrects X/Y position. With a scale of greater than 1, the dragged item grows to encompass the whole screen.

It seems that a calculation that should be happening once to correct for the scale is instead happening continuously and cumulatively.

This behaviour does not appear to exist in 1.9.0.

JSBin/JSFiddle demonstrating the problem:

Demonstration of draggable item shrinking exponentially:
http://jsfiddle.net/GBorreson/m549v1t0/6/