HTML export turns into cpgz
This issue can happen, if your server's zipping program is outdated, and you are using Mac, which doesn't have a widely usable unzipper program by default. You have to either contact your server host to update their zip program or try out 3rd party apps, like BetterZip or Springy.
So this is not something, that could be modified in our code, and the problem isn't coming from us! Use google, if you want to see other discussions about this very common Mac issue.