Duplicate image after upload

Hello,

When I upload an image file with drag and drop in the specific zone, the image is stored on my server twice and shwon twice on the uploaded image list. Checking with firebug, I can see two requests.

But, if I select an image using windows explorer ( after clicking on drop zone) or if I drag/drop the image on the right side of asset manager, where you can see the list of uploaded image, the image is uploaded once. Checking with firebug, I can see only one request.

Thank you for your help.