Why does Boolean difference add material to this mesh? In Blender 2.76b and 2.79b, in a mesh, I have added a Boolean subtract modifier. The subtracting mesh was made from text. I have another mesh from text which subtracts correctly. However, on this one, instead of only subtracting the volume, it also adds an outline where the modifying mesh (from text) exceeds the modified mesh.

Here is a screenshot showing the modified mesh in edit mode:



Here is a screenshot showing the modified mesh, in which you can see that the subtracted mesh (from text) somehow also adds:



I mirrored some of the vertices in making the modified mesh, because the shape I am making is symmetric. Mesh from text subtracts correctly on the first side which I modeled by hand. However, mesh from text (whether I duplicate the first text or create new text) adds as well as subtracting on the mirrored side.

Does the mirroring have anything to do with this? How can the issue be resolved?

Here is the .blend file.

Thank you!
Seems to be an issue with the "Carve" Solver. When I switch to "BMesh" in Blender 2.79b, it seems to produce the correct output. Thank you for providing ideas!