Expected "frame rate" when minimized with "Run in background" enabled?

If a game has "Run in background" enabled, and the app is minimized, it seems that the MonoBehaviour Update-methods will be run at a very high rate (possibly thousands of FPS, at least on Winows). We've been getting reports from our users on high CPU usage when minimized, which we haven't been getting before.

Has there been a change in Unity regarding this?
What is the expected behavior?
Is there some clean way to limit the rate when minimized, if we want to keep "Run in background" enabled?

 

I'm seeing this behavior in 5.3 and 5.4 betas, did you ever figure out what was causing this?

 

I managed to get the some profiler data by connecting to a standalone build.

When application has focus (250 fps):


When application doesn't have focus:


Performance is very erratic when not focused. I'll strip down a repro case for submission and leave a ticket number here soon.

Edit:
Found an active issue on this topic: https://issuetracker.unity3d.com/issues/framerate-is-not-capped-while-running-in-background