Well because its only the active matrix, I am thinking the early transistors are going leaky on the internal plane. Either that, or LCD contamination due to bad edge seals. This fabrication process may have changed on the color displays so you dont see these faults.

All liquid crystals require AC drive, otherwise the pixels will supertwist and get stuck on, then fade.... Also when applied to DC, the liquid crystal begins to take on a di-electric property and hold a charge, and when the DC is removed it takes a bit for the charge to leak off. Which is what is happening. Also if the potential is high enough on DC it can actually damage the LC. This is why typically liquid crystals are driven with an AC signal.

im beginning to think its because the transistors are going leaky, so they are causing a DC bias on the AC signal. which is bad news for liquid-crystals.