intel hd3000 "driver" bug?

Hello,

i have an external Monitor (27") from Dell which is connected to my MBP 13" (non-retina) late 2011.

Sepcs:
2,8 GHz Intel Core i7
8 GB 1333 MHz DDR3
Intel HD Graphics 3000 512 MB
OS X 10.8.4 (12E55)

Diagnostics:
Intel HD Graphics 3000:
Chipsatz-Modell: Intel HD Graphics 3000
Typ: GPU
Bus: Integriert
VRAM (gesamt): 512 MB
Hersteller: Intel (0x8086)
Geräte-ID: 0x0126
Versions-ID: 0x0009
Monitore:
Farb-LCD:
Monitortyp: LCD
Auflösung: 1280 x 800
Pixeltiefe: 32-Bit Farbe (ARGB8888)
Synchronisierung: Aus
Eingeschaltet: Ja
Integriert: Ja
DELL U2713HM:
Auflösung: 2048 x 1152 @ 60 Hz (this is wrong, it's set to 2560x1440!!!)
Pixeltiefe: 32-Bit Farbe (ARGB8888)
Monitor-Seriennummer: ***********
Hauptmonitor: Ja
Synchronisierung: Aus
Eingeschaltet: Ja
Rotation: Unterstützt
Verbindungstyp: DisplayPort
Fernseher: Ja


For the connection, i use a mini Displayport to Displayport cable.
If i set the Resolution to 2560x1440, i get a lot of blackouts on the external monitor (every 20 seconds, at least 2 seconds long).

What i know is:
it is NOT the Monitor (it's working with a 15" mbp with different graphic card; furthermore i got two dell-screens, same issue on both)
it is NOT the cable, i tried 4 different from different production-companys.

What i did:
i reseted the smc and pram with no changes.
i tried Apples mini DP to dual-dvi adapter (99$) which has the same problem.

What is working:
It is working under Windows 7 (Bootcamp) without problems!
It is working, as soon as i close the MBP and use only the external monitor!!!
It is working with lower-resolutions.

I googled a lot today but couldnt find People, with the same problem.
So, any ideas??


Thanks in advanced!