Interestingly, I have a Lenovo Thinkpad docking station at my office which also uses DisplayPort technology (
possibly this one). It is connected to one monitor. When I went to office today and connected that station to the laptop, it got detected fine and worked alright. Now I am back at home, and the Targus box is still showing the same behavior: only keyboard and mouse gets detected.
Not sure what to make out of all this.