encoder problems......

[alb4h]

We are having a problem that occurs when plugging in an encoder.

The encoder is wired into 2 digital I/O ports on the digital sidecar, with careful attention made to plugging in gnd and signal to one port and 5v and signal to other port. The problem occurs even when plugged into any 2 ports.

With the encoder wired, when the code is enabled, and in teleop mode, the motors start to run, with no joystick input.
With the encoder unplugged, everything works as expected, with no movement until the joystick is moved.

We are using C++ and this happens even when deploying the FRC Default Program (current with imaging tool), which when loaded into workbench is titled BuiltinDefaultCode.
That code does not explicitly reference digital input ports or the encoder classes at all.
Why does hardware plugged into the digital I/O ports effect the motor control?

I'm confused.......

Ann