UI camera not matching main camera in VR

I am currently using a separate camera to ensure that the UI always renders on top of objects in the scene. It is a child of the main camera, so it matches its position and rotation. This works fine when not in VR, but in VR the menus look like they're rotating counter to the head tracking (the menus are world space canvases with the same parent node as the main camera.) My guess is, either the menus are rotating in response to the main camera's rotation, or the UI camera isn't matching the main camera's rotation. Does anyone know what might be going wrong?