Turning off smooth lighting turns model cubes rotated ±22.5 degrees dark

Hard to tell if this is intended behavior or not, but turning off smooth lighting turns all cubes rotated ±22.5 degree dark. Does not affect cubes whose faces are aligned with the 90-degree angle grid (0, 90, 180, 270).

Adjusting ambientocclussion, shade, and cullface doesn't correct/affect this.

The example screenshot is of my loom model, the first being with smooth lighting on (minimum or maximum, either works), the second with it off. The strings are the only cubes rotated ±22.5. This affect is not limited to this one model. It affects all models that I've looked at.