string literal error?

[badmadevil]

Hi, sorry if already discussed.

codes:
   string x = "bug?" ;
   string y = "bug?" ;
   string z = "bug?".reverse ;
   writefln("%s : %s : %s", x, y, z) ;
   x.reverse ;
   writefln("%s : %s : %s", x, y, z) ;

output - D 1.027 & 2.013:
 >?gub : ?gub : ?gub
 >bug? : bug? : bug?

Should x, y, z be independent to each others?