Clone command is execute even if the clone is the same.

I make a map of spleef who is regenerated with a snow disc pattern cloned by the clone command.
In 14w10b the clone command use replace only blocks who are not the same but now it replace all the block of my pattern causing big lag with Lightning Calcul needed.
Command : "/clone 390 48 350 422 48 382 466 127 278 masked"
When i try to clone my pattern when blocks are alredy here.
14w10b : No blocks cloned.
14w10c : 861 blocks cloned.
14w19a still to clone non air block even if they are the same (with 'masked' mode).
Still occurring in 1.8
Still occurring in 1.8.1-pre3