I've searched a bit around the internet to find a solution for my automatic standby not being invoked on my notebook and haven't found a solution until now.
Unity3D has been created an audiostream which prevents Windows from automatically changing into standby.
>powercfg -requests DISPLAY: None. SYSTEM: [DRIVER] Realtek High Definition Audio (HDAUDIO\FUNC_01&VEN_10EC&DEV_0283&SUBSYS_10250864&REV_1000\4&1e5ed8f7&0&0001) An Audiostream is currently in use. AWAYMODE: None. AUSFÜHRUNG: None. PERFBOOST: None.
After closing Unity3D everything returned back to normal:
>powercfg -requests DISPLAY: None. SYSTEM: None. AWAYMODE: None. AUSFÜHRUNG: None. PERFBOOST: None.
why? I don't know. Maybe Unity reserves an audiostream for future use or something like that.
So if you're a Unity developer having issues with automatic standby try closing Unity before being away for a long time.