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Rotation about crosshair rotates about the crosshair position in the unrotated base image. There is not a good fix for this issue. If the current cursor position in the rotated image is calculated for rotation about crosshair then then it will cause image jumps when the angles are changed after a cursor location change, or you get image jumps when switching to about crosshairs when a rotation is applied. The current position in the rotated frame is complicated to compute, so it is easier to accept that rotations about crosshairs must start from an unrotated base image.

Overlays shift relative to the base image during rotations.

• world co-ordinates
  • center rotations shift
  • origin rotations static
  • crosshair rotations shift
• index co-ordinates
  • center rotations static
  • origin rotations shift
  • crosshair rotations static

The amount of shift depends on the ratio of the overlay voxel size to the base image voxel size which suggests that the problem may be related to rounding issue in conversions between world and index co-ordinates. Because the different voxel sizes, if you compute a rotation about a voxel index it would be a different rotation in the two cases.