Qt 5.2.0; OS Windows 8; x86 architecture.
Test case:
Reproducibility: 100%

Steps to reproduce:
1)Build and run test case
2)Drag red rectangle to coordinates (x, y), where x < drag.threshold and y < drag.threshold. In this testcase drag.threshold = 20, so you can drag red rectangle to point (15, 15) for example. Drop rectangle.
3) Try to drag red rectangle to the left or to the up or to the left corner of the blue rectangle.
Result: You can not move red rectangle in these directions.