If I upload an image A.jpg and wait for the image to be uploaded the block is created.
But if I try to reupload it once again it doesn't work and there is no error displayed.
If I upload another image B.jpg it works and then I can reupload A.jpg if I want.
In a way, it's kind of a great feature to prevent people from uploading the same image twice but I think it should at least display a message.