[ozrien]

One more thought...
In hindsight, a better approach to debugging this might have been to un-deploy code so that the robot is in the no-code state. Then use the Self-Test in the roboRIO web-based config to measure the sensor position, move one rotation, and hand-calc the difference to confirm the right number of ticks. Probably a good trick to ruling out robot-side influence on future problems involving decoding sensor. Wish I had thought of that earlier, oh well.