Sitecore 8, as recently as build 150427, has an issue unpacking zip files uploaded into the Media Library. This fix is to patch your Website\sitecore\shell\Applications\Media\MediaFolder\MediaFolder.js file with the following:
this.yUploader.upload(file, this.destination, "POST", params);
this.yUploader.upload(file, this.destination, params);
Thanks to the Sitecore Community for sharing the results of their bug reports.