I have a face which is a trimmed bspline surface. When the face is not tessellated I get a very large bounding box, and when it's tessellated I get the correct smaller bounding box. I think it's a bug BndLib_AddSurface, the code is:
if (Abs(UMin-S.FirstUParameter()) Abs(VMin-S.FirstVParameter()) Abs(UMax-S.LastUParameter ()) Abs(VMax-S.LastVParameter ())
the "if" sentence always give true back.