Created attachment 62383 [details]
Simple test case of bug. Drag the image. The dialog that pops up should say 1 = 1. It currently says 1 = undefined.
The DragEvent.dataTransfer.getData(format) returns undefined when DragEvent.dataTransfer.setData(format, data) was used immediately preceding. See http://decafbad.com/2009/07/drag-and-drop/api-demos.html#data_transfer for an example of this failing. Alternatively, the attached file calls DragEvent.dataTransfer.setData('text/plain', '1'), and then alerts DragEvent.dataTransfer.getData('text/plain'). Currently, it alerts that it it undefined.
I think that this is a duplicate of https://bugs.webkit.org/show_bug.cgi?id=23695
Using the latest nightly, r152754 built on 17 July 2013, I am seeing 1 = 1.