Why is my Smooth tool causing the surface of my sculpt to be reflective? While sculpting something - inexplicably after I boolean joined two meshes - the newly joined mesh has an issue where the smooth tool will cause the normals to become reflective!

I've tried recalculating surface normals to no effect. What the butt is going on?
The culprit is actually the Solidify modifier. When i applied the mirror I was under the impression that i needed to use solidify to make the mirrored geometry physical.

Solidify will make an internal geometry. when sculpting, i would only be hitting the upper mesh and it would clip through the lower.

Lesson learned: do NOT solidify objects you intend to add to a sculpt.