summary: Spark-shell fails to redefine values in some cases, this is at
least found in a case where "implicit" is involved, but not limited to such
cases
run the following in spark-shell, u can see that the last redefinition does
not take effect. the same code runs in plain scala REPL without problems
scala> class Useless{}
defined class Useless
scala> class Useless1 {}
defined class Useless1
scala> implicit val eee :Useless = new Useless()
eee: Useless = Useless@2c6beb3e
scala> implicit val eee:Useless1 = new Useless1()
eee: Useless1 = Useless1@66cb003
scala> eee
res24: Useless = Useless@1ec5bf62
