Cinemachine - Weird rotations when blending between two cameras?

I'm creating a game about traversing the surface of a cube, and when transitioning between faces I'm blending between the current virtual camera, and a rotated clone. For some transitions this works fantastic, but for others, Cinemachine adds this weird rotation around the camera's local forward.

https://youtu.be/0glnUl2uN5E

As seen in the video, the first and third transition work as planned, but the transition to the back face, and the transition to at the end have this issue. I've tried, but couldn't understand why this is happening. I've debugged the transforms of the two cameras, and mathematically, the most efficient transition should always incorporate a rotation around one axis only, yet for some reason this anomaly occurs.

Is there something I've missed that could cause this issue? Or perhaps a way to constrain the blend? All help appreciated!