Root bone rotations for NPC animation don't work the same as for creature animation

While in the vanilla engine they work the same, in openMW WalkForward animations give different results when using the same animation for a creature and for a NPC (it's basically the Guar animation with a NPC version of Lidicus' rider animation made for this mod). It works perfectly for a creature, but the NPC rotates back and forth during every walk cycle. The only time the creature rotated the same way was walking in place trying to reach a space already occupied by another actor. The root bone animation is the cause since the issue isn't visible when using "Playgroup walkforward 1" on the NPC.

To reproduce, here's a smaller test case with NPC and creature using the same files: mountedguar2test.7z - "coc Vivec" and look at the bridge on your right. With the vanilla engine to see the proper animations on the guar with the NPC (technically unrelated to the issue but it's there to easily compare with the creature) you need MCP feature "Improved animation support".