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.