C4DtoA 2.6.1 [4186e70b]
Arnold core 22.214.171.124
The title of this post describes most of the issue. More below...
New scene. Create a camera. Create a cube. Make sure cube is below camera object in hierarchy. Set IPR camera to the camera object. Move camera object in hierarchy below cube object. IPR camera should be forgotten / revert to default.
Set IPR back to the camera object. Move the camera object back up above the cube in the hierarchy. The IPR doesn't forget the camera this time correctly.
Another part of the problem is this:
With the camera object below the cube in the hierarchy and the IPR set to the camera object, move the camera around in the viewport. Now undo that movement. The IPR should forget the camera because it was below the cube in the hierarchy.