LOW does not equal 0V

I have built myself a PWM driver comparable to http://www.flickr.com/photos/hoeken/2487838735/sizes/m/. While everything works as a charm I noticed something odd: When setting Arduino PWM-pin 6 to digitalWrite 0, I am still seeing faint light coming from the control-LED (LED 1 in the schematic). Potential over this control-LED is a little over 0,6V. After switching to another PWM-pin the control-LED is off and the potential is 0V.

After checking my circuit multiple times and changing a couple of parts the result were the same...

I decided to check the output from my Arduino (I/O pin 3, 5, 6, 9, 10, 11) by means of:

1.) analogWrite(pin,255) 2.) analogWrite(pin,0)

All pins, except pin 6 and pin 11, have a range from 0V to 5V. Exactly what one would expect.

Concerning pin 6; lower limit=0,1V and upper limit=5V. Concerning pin 11;lower limit=0,1V and upper limit=4,2V.

I double checked using digitalWrite. This gave the same results.

Are there any, thinkable, reasons why pin 3 and pin 11 deviated from the other pins?

The pin 6 issue is because the timer generating the pwm on that pin is also used for the millis() function, so the PWM uses a different mode (fast PWM instead of phase correct). Not sure about pin 11; that's weird. Anyone have any ideas?