Game Download Pauses Automatically When Playing

Apparently if I run a game it pauses the current downloads.

I found out after I'd started a 30GB download and then went to play something for several hours only to then see that the download I assumed would be finished already was paused 5MB in.

I'm guessing this is to help me avoid online lag in the offline, single player game I was playing.
Please don't do this, or at the very least, add an option to disable it.

It should be disabled by default, really.
You can tell if you're lagging while playing.
You can't tell if the download you started that's supposed to be running in the background decided to pause on its own without telling you.

Totally wasted my day.