CCScale9Sprite setPreferredSize when the size is smaller than the size, eg: CCSizeZero the display will be not correct.
I have this problem also, but from what I read CCScale9Sprites aren’t displayed properly when size is set to smaller value than the CCScale9Sprite original size. So this probably isn’t a bug, it’s just a feature 
But cocosStudio using it for UILoadingBar like ProgressBar, UILoadingBar bug??