Seems Patch 1.10 wasn’t all honey and sweet after all.  The Blizzard Background Downloader has a broken feature: It can’t disable the background downloader because preferences won’t save.  A Blizzard Dev offers a temporary workaround that requires you to download registry files into your Windows Registry.  Scary o’s!

MichaelKN : The Background Downloader simply pre-fetches the patch data (if available) so that on patch day, you will have the majority of the patch already downloaded. The data will not be applied to the game until patch day. Also, the Background Downloader will only launch and run when/while you are playing World of Warcraft. If you do not wish to use the Background Downloader, you may disable it in it’s preference menu – you may re-enable it again later if you ever change your mind.

*If you have a firewall installed, it will most likely warn you with a pop-up message on when the Background Downloader starts.

We will release an FAQ regarding the Background Downloader in the near future. Be sure to keep an eye on our sticky for any updated news.

DatTH: That part of it is currently broken. I have posted registry settings that will disable it properly. We are currently aware of an issue where the Background Downloader won’t save a user’s preference settings. We have some registry keys available as a temporary workaround. To apply these fixes, just download and apply these registry keys. They will take effect the next time the Background Downloader starts up.

Disabling the Background Downloader: https://ftp.blizzard.com/pub/WoW/other/disableBGD.reg
Enabling the Background Downloader: https://ftp.blizzard.com/pub/WoW/other/enableBGD.reg
Disabling Peer to Peer alone: https://ftp.blizzard.com/pub/WoW/other/disableP2P.reg
Enabling Peer to Peer alone: https://ftp.blizzard.com/pub/WoW/other/enableP2P.reg