"adb shell am set-inactive <package name> true" does not work

Question

I want to check application standby. The devices I use are the edge of the Galaxy S7 and a virtual device with Android 6.0 (API level 23).

I use:

$ adb shell dumpsys battery unplug
$ adb shell am set-inactive <packageName> true

When I test whether the application is really in standby mode using adb shell am get-inactive <packageName>, I always get the following result Idle=false. Has anyone else experienced the same behavior?