Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
If you think it is a bug, then post to the bugs forum for faster attention. You can even label it "Possible Bug ..." if you are not sure. If it is a question about command usage, then post to the appropriate forum for that API. Don't worry about the double post. This seems to be a bug or a change, if it was working before. But the IM developers or one of the Windows users will have to check into that. I do not use Windows, so cannot check for you.