If you set the NoAI tag for a guardian that is charging his beam to 1, the beam of the guardian will be in a much longer range, will not disappear, will not damage the player and the guardian's body will still track the player (But won't move, just look at the direction of the player). The guardian's beam will also track the player in creative mode and spectator mode. The guardian's beam can also track the player even if there's a wall in between them.
What I expected to happen was...
The beam of the guardian would disappear and the guardian's body would stay still.
What actually happened was...
The beam of the guardian stayed and the guardian's body faced the direction of the player.
Steps to reproduce:
1. Summon a guardian.
2. Go into survival mode.
3. While the guardian is charging his beam at you, enter this command: /entitydata @e[type=Guardian,c=1]

A video of the issue occurring: https://youtu.be/4yF1WCvOYNI