System Information
Operating system: Win10 64bit
Graphics card: GTX 1050ti

Blender Version
Broken: 2.79b

Short description of error
Armature has baked action in two modes: XYZ and Quaternions.
XYZ at frame 4 has a shift in rotation (preventing gimbal lock?). In viewport they both look identical, but sampled motion blur is very different

Exact steps for others to reproduce the error
Open file and render, then switch to another render slot and select Armature_XYZ in Cube's Armature modifier, render another time and compare results.