Those kinds of erasers are best used for things like charcoal, so when used on standard 8x12 printer paper, it tends to shred. My suggestion is that you tear off a small piece of the easer and use a lighter touch when erasing.
That will also happen when you try to erase too fast. Slow down and take your time with it. As tempting as it is, this isn't the kind of eraser you press into your lines and scrub away with all your might. It takes a deft hand. Plus, that way, you'll be able to conserve materials overall. :)
It's strange though because the last Prismacolor kneaded eraser I used (on a Blick sketchbook and Bristol board) worked normally even if I applied a lot of pressure or erased fast. I guess they're all made differently, even from the same brand. Or it got fried during the shipping.