When sharpening my pencils, the 4H, 2H, H AND 2B went just fine. But when I tried to sharpen the B pencil, about 1/2 cm or so, the graphite was broke all the way through the pencil and just slipped out of the wood. Is this common or just a low quality brand? I have a couple different brands. This is my Artist's Loft Pencils.Details