Can the voltage drop of an LED driven at a constant current be higher than the supply voltage?
Can someone explain what's going on here? How can the LEDs draw more
  current than the voltage drop across them in series should allow?




Each LED with typically (say) 3 volts across it and (say) passing 110 mA dissipates a power of 330 mW. For the green LED it will warm at a rate of 69 degC per watt hence, it will warm from an ambient temperature of (say) 25 degC to 48 degC.

As the local ambient rises around each LED (due to this heat being dissipated) this causes the forward volt-drop to fall at 3 mV / degC.

So, making an estimate of the total LED temperature rise being 50 degC, the forward volt drop will fall from typically 3.15 volts to 3.00 volts. But, there's nothing to say that all your LEDs are bang-on middle-of-the-road typical and, the batch you received may indeed have a forward volt drop of closer to 2.80 volts.

In other words, it's not beyond any stretch of the imagination that the volt drop you see across each LED is below 3 volts - theoretically it might begin (when cold) at 2.80 volts and drop to 2.65 volts when fully warm.