That seems to happen to the new zipped content when using Internet Explorer - try using a different browser (you don't have to make it your default if you prefer IE) to download. I think safari may also be affected - Firefox and Chrome should be OK. Note that if this is a zip, the files will be in a Content folder which you may not want - you will need to extract them from that and place them in your actual content directory, such as the My Library folder.