arabesc,
I had the same sleep issue over Displayport (see here). I exchanged the monitor and the new one does not exhibit this issue. So it appears to be a problem with certain batches. I recommend that you exchange yours as well.
Received this monitor last week and it is great. However, I am experiencing a strange issue with standby/sleep mode when connected via Displayport. Basically, if my computer goes to sleep or is turned off, the monitor will not properly go into sleep/standby. The backlight will initially turn...