Sympathetic resonance, I think. Any real pause in playing while both halves are on means you get a bit of noise... depending on the situation, that can be a cool addition (subtle harmonics or drones) or an annoyance (extra squeal). You can shut one set of pickups off via the master switch, but sometimes you dont have time to flip the switch back and forth. So I tried using a cheap gate pedal when I needed it to go silent for a second or two, and that's worked really well.

As for the purchase issue... well, I bought it after watching Ebay for like a year, heh. Sold off some lesser used ones in the process.