Operating system: Linux-5.3.0-29-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.59
Broken: version: 2.82 (sub 6), branch: master, commit date: 2020-02-11 14:45, hash: rBc939b4df18e9
Short description of error
The 'look' of motion blur changes (e.g. frame 1 and frame 2) based on the interpolation mode used, despite there being no room to interpolate between the frames.
Above are frames 1 and 2 of a test animation. The cube is parented to the 'child' bone (using the armature modifier). The 'child' bone is parented to the 'parent' bone as an armature relationship.
All of the bones of both armatures have exactly the same keyframe values, but the interpolation mode of the child bone is different. In the top rig, the child bone has 'constant' interpolation. In the bottom example, the child bone has 'bezier' interpolation.
I can understand why the interpolation mode will have an influence on the look of motion blur of keyframes not directly next to each other, but neighbouring keyframes like this should give exactly the same result as there's no room for interpolation.
Exact steps for others to reproduce the error
- Open 'blur-test.blend'
- Hit render