Win7 Ult x64 Sp1 + GeForce 880 GTS 512
Similar result on another (newer) machine with Win8.
Broken: 2.71, 2.70
Worked: 2.69 (supposedly based on blendernpr.org tutorial)
Short description of error
In freestyle, all splitting options work normally except for 'Material Boundary'.
Exact steps for others to reproduce the error
With Freestyle activated and the following setup in Properties > Render Layers > Freestyle Line Style.
Chaining checked, all others unchecked
+ Thickness modifier 'Along Stroke'.
Checking Material Boundary seems to split some lines at angles even when min and max 2d angle are deactivated.
Test file available for 7 days on