Windows 10 Radeon HD 4800 series
Broken: 2.79.2 4b206af
Worked: 2.79.2 a3409d3 (or any build prior to carve being removed)
Short description of error
Well, bmesh flat out fails in cases when carve did fine with co-planar geometry.
Exact steps for others to reproduce the error
Just add a boolean modifier to 2 prongs object and that's it