Collider/trigger collision causing physics glitch

Player character with Rigidbody/Collider setup. Large Box collider set as Trigger. Using custom model with Standard Assets animations (Ethan). Issue discovered in Unity 5.4.4, no change in 5.5.1. Unity 64 on WIndows 10 64bit

Issue: When the character passes through the Trigger bounds, occasionally the character is bumped off-screen. Simply passing through is inconsistent, but turning the character repeatedly at the edge of the trigger causes fairly consistent occurrence.

I've tried adjusting the Trigger and the Collider and scripted behaviors regarding collisions and Raycasts, all to no avail. I do plan on creating custom animations and maybe that will fix it, but I doubt it.

Any help would be appreciated. Thanks.

Update: I've discovered that colliding with the trigger at right angles seems to avoid the glitch. Narrower angles, however, are more likely to cause it. Near-parallel movement (along a surface, not jumping) through the trigger boundary is virtually certain to cause it. I have one trigger at zero rotation on an incline that glitches more often than another on a virtually flat plain.