Welcome to CASC. this has been a bug for all casc games for a long time. it now affects Diablo (2.2.0 and later). Wow 6.0 and later. Heroes of the storm.
Only a matter of time before SC2 and hearthstone switch to casc and gain the bug too.

It is mac only, and was a "known issue" like a year ago but since it's a mac issue, low priority unless it's game breaking. This isn't game breaking, just a grave annoyance. My Wow Updates 2-3x a day. By updates, I mean reconfigures indices, and downloads about 15mb patch file over and over again. Same file, same md5. Just over and over again. I got to point i set ANY and all games that are casc to manual updates only, so at the very least, they only update when i play them (after clicking update, as you do). vs letting them automatically patch themselves pointlessly multiple times a day, every day.

This is a bug with server configuration as far as i can tell. The server updates the configuration file, and our clients think there is an update as a result of it. The server update configuration at least twice a day from what I see. I have currently found no way to avoid bug. locking files breaks launcher. bypassing launcher doesn't fix it either, because the game binaries themselves are coded to check same configuration file on launch and if THEY see the false update, will either download it themselves, or exit and tell you to open launcher first. I've tried blocking the url to update server, and the applications refuse to open or connect if they cannot check for updates.