Using FLANN with binary descriptors (Brief,ORB)

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I am trying to use FLANN with binary descriptors (brief, orb) with no luck. My code looks something like this:

vector<vector<KeyPoint> > dbKeypoints;
vector<Mat> dbDescriptors;
vector<Mat> objects;   

/*
  load Descriptors from images (with OrbDescriptorExtractor())
*/

FlannBasedMatcher matcher;

matcher.add(dbDescriptors); 
matcher.train()              //> Crash! (or any call to matcher.match())

If I use SurfDescriptorExtractor() it works well.

How can I solve this?

OpenCV says:

OpenCV Error: Unsupported format or combination of formats (type=0
) in unknown function, file D:\Value\Personal\Parthenope\OpenCV\modules\flann\sr
c\miniflann.cpp, line 299

(Note: i have posted the same question on stackoverflow)

I have found an hacky solution but i think it's not so good here

Basically the author before adding to FLANN converts the binary descriptors to CV_32F. But i don't think it's good beacuse distance must be calculated with HAMMING distance, and not euclian distance with float values.