cv::gpu::blur returns zero Mat when Mat is processed in place

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With cv::blur on CPU you can process cv::Mat in place like:

// have defined and filled cv::Mat my_mat
cv::blur( my_mat, my_mat, cv::Size( 4, 4 ) );

If I try the same thing with cv::gpu::GpuMat and cv::gpu::blur like

// have defined and filled cv::gpu::GpuMat my_mat
cv::gpu::blur( my_mat, my_mat, cv::Size( 4, 4 ) );

my_mat is now just all zeros, i. e. black.

If I create an empty GpuMat header, pass it to blur and assign to Mat everything again works like CPU example:

// have defined and filled cv::gpu::GpuMat my_mat
cv::gpu::GpuMat tmp;
cv::gpu::blur( my_mat, tmp, cv::Size( 4, 4 ) );
my_mat = tmp;

I think this is a bug in cv::gpu::blur, isn't it?

I am using ubuntu 12.04 64 bit with cuda 5.5 and OpenCV 2.4.7