That鈥檚 not a bug. It鈥檚 a feature that was added a long time ago, but it was broken for as long as I can remember. 
I fixed it two months ago in FIX: Outgoing emails were not disabled after restoring backup 路 discourse/discourse@dc961fe 路 GitHub
You can disabled that behavior when you restore from the command line:
discourse restore --disable_emails=false <filename>