I know that the proposition $$ A \text{ is a UFD } \Rightarrow A[[X]] \text{ is a UFD }$$ is false.
Wikipedia states that if $B=K[x,y,z]/(x^2+y^3+z^7)$ then $A=B_{(x,y,z)}$ is a counterexample, but I can't show that $A$ is a UFD and $A[[X]]$ isn't.
Are there other known counterexample?