Shulkers sometimes "flinch" when the player is in close proximity

Sometimes, shulkers will "flinch", where they open up to shoot you, but get interrupted for no reason and close before they even are completely open. During this behavior, they tend to be open for much less time than the norm (i.e. during peaking behavior). This occurs most often when a shulker is first alerted of the player's presence, but can occur any time the player is within range.

Possibly an intended feature, but doesn't seem that way.