Question about integrity of Blind Signature

[Chein-hsinLiu <r3506010@cml11.csie.ntu.edu.tw>]

  Hi!
I have some question about ecash protocol. In ecash protocol, we represent
money by a sequence number which is signed by bank. And for privacy, we
use blind signature. But when we send bank a pesudo sequence number--
X*PK(r) (X:sequence number we want, r :random number to cheat bank)
then we can get SK(X*PK(r)) from bank, and get money by SK(X*PK(r))/r=SK(X).
But if we divide SK(X*PK(r)) with r', we can get another money? It confuses
me. How does it preserve the integrity of the money, and let people divide
r on the SK(X*PK(r)) ?
  It confuses me very long time. Thanks for any help!
  Chein-hsin Liu 4/1/96