Has anybody else noticed this? With any amount of "Drift", the oscillators act just like any analog VCO, that is, they are free-running and any keypress will open the VCA with the oscillator at whatever phase it happens to be.
However, with Drift set to zero, the oscillators will sync to their zero-crossing point with each keypress. This is good for eliminating the random "pop" that happens at low frequencies with very short attack times. Handy, I think undocumented, and something I wish analog synths would make available. The only other synth I know of that can do this is the Virus, and it's also not analog.
A minor drawback to this is that if you are using more than one oscillator and they are slightly detuned, you will get an unexpected sync at the start of each note which quickly ends - bottom line, don't turn the drift to zero in this case :-)