#currently you are doing this (effectively)
a = {:action => "list", :notice => "yay"}
redirect_to a
#you want to be doing this
a = {:action => "list"}
b = {:notice => "yay"}
redirect_to a, b

#which you can do by explicitly adding the braces around the URL stuff, like so
redirect_to {:action => "list"}, :notice => "yay"