Orientation Visualizer doesn't show pitch & roll properly

The Processing-based orientation visualizer examples doesn't display properly. Pitch and roll are only shown independently when yaw is 0 or 180 degrees. When yaw is 90 degrees, they display the same!

I made this video demo to show the problem:

https://www.youtube.com/watch?v=SHJ2n1Kwe58

Here is the page where the orientation visualizer code appears.

https://www.arduino.cc/en/Tutorial/Genuino101CurieIMUOrientationVisualiser

Start with the Processing-based visualizer linked from the Genuino101 Curie IMU Orientation Visualiser page and compare its behavior with the linked video. Trace how pitch, roll, and yaw are displayed, then verify that pitch and roll remain distinct when yaw is 90 degrees as well as at 0 or 180 degrees.

Written by the indexing model from the issue text.