TalonSRX uses encoder when not in Voltage mode

[while1fork]

We have been trying to read an encoder connected to a TalonSRX. We have it in voltage control mode, but are trying to read the velocity from the encoder.

However, we have come across some behavior that we can't understand. When we have an encoder plugged into the talon, even when the talon is in voltage control mode, it causes the talon to make the motor jitter and move slowly. The talon works fine if I remove the encoder (without changing the code).

Why is the encoder affecting how the talon works when the code tells it not to use the encoder?