ART - Knee popping when character is posed in seated position

I’ve rigged and animated a character with ART, and getting knee popping when character is posed in a seated position. I noticed how just animating the IK foot in the Z axis causes the knee to jump position over a frame.
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To make sure it’s not just how I rigged the character, I tried it on the default Mannequin and get the same results. I’ve attached a simple animation showing this issue.


  1. Add Character for animation - Mannequin
  2. select body_anim control, and put into seated position (trans x=44, y=52)
  3. select ik_foot_anim_l control - at frame 0 key trans Z=-2 - at frame 20 key trans Z = 2.
  4. change camera to front view, and notice the knee popping at frame 11.

I first noticed this happened when repositioning my character to be offset from the root by selecting all the IK controls, and even with the hips in the same relative position, the knee still pops.
The issue is less pronounced when the hips are higher in the z axis, but still there.

Softtware Version - Maya 2016 Extension 1 + SP6 (also tested in Extension 2)
Using ART with latest dropbox updates applied.

I’ve asked this question on UDN now.