In the above setup, a plane in material editor rotates along -1,0,0 as expected, since RotateAboutAxis will turn 1,0,0 into -1,0,0 when RotationAngle is 0.5, or 180 degrees.

In this second setup, only RotationAngle is changed to 0.25. NormalizedRotationAxis for the second RotateAboutAxis function is expected be 0,1,0, as such the plane should rotate along the y-axis. However, from what I observed, the plane is rotating along a changing rotation axis. My goal is to have position of the first RotateAboutAxis as a variable vector on the xy plane, find an orthogonal vector to this variable vector in the xy plane and use this orthogonal vector as my rotation axis.

Am I using RotateAboutAxis wrongly here?