Any release from 2.71
Windows 8 64bit and Windows 7 64bit. Intel CPU on both systems. Tested with and without OpenCL on Windows 8.
Bounding box input takes a mask to restrict area blur is performed on. This stopped working in the 2.71 release.
Steps to Reproduce
Open the attached blend file in any release from 2.64 to 2.70a and composite. A backdrop image should appear with a small patch corresponding to the mask blurred. This is the correct behavior.
Now open the same file in any version from 2.71. On my system blur is applied across the whole image without respecting the mask input.