Hello !
We have a mesh with some sharp edges and, sometime, computing signed distance around these edges return a wrong sign. If I have understood correctly, sign is computed using orientation of the closest triangle and in the case where closest point is on a (very) sharp edge, a "wrong" triangle can be used (just see attachment, it will be easier to understand).
Anyway, it is not a big problem for us because we will always try to use relatively "smooth" meshes but for your information...