Question Animator problem when adding animation layer

Hi all. I have an animator with root motion enabled and it all works fine until I add an animation layer. It does not matter what's in the new layer, but as soon as I add it the game object starts moving up! The only way around it is to only have the base layer, disable root motion or change "update mode" in the animator to "Update Physics". I am trying to understand where the extra root offset is coming from and why it is happening.
Here's a video of what's happening: