Hi, this is a standard paperweight fracture that shows up most frequently with older weights,
I own several paperweights with this kind of fault. These fractures are easy for collectors to spot,
but can be mistaken for something else by someone not versed in paperweights.
The silvery sheen is what you expect to see when a fracture is present.
There is no doubt in my mind that this is a fracture.
It is most assuredly not designed that way, and happened due to either improper annealing as Glasstruffle pointed out,
or some kind of external stress ( ie temperature swings, falling off shelf etc.)
Glass is a very interesting material and behaves strangely sometimes, you can have all kinds of fractures throught a
paperweight yet it stays in one piece, and might not show any surface faults at all.