Cinemachine Free Look with Collision has odd motion in corners

[Unity 2020.2.4f1, Cinemachine 2.6.3]

I have a Cinemachine Free Look camera setup with a Cinemachine Collider attached. The collider strategy is set to Preserve Camera Height. When rotating the camera on the bottom rig the camera collides with the wall as expected, but when I rotate past the corner behind the character (blue ball) the camera appears to move first down and then back up the wall (breaking the strategy to preserve camera height) and then continues along the rotation path. Note: the columns that pass through the camera line of sight are tagged to be ignored.

Video of scene/game/inspector view of the collision problem:

Any suggestions for settings that might alleviate this motion in the corner?

Thanks,
Aaron