Thank you, I've found the solution to my problem here:
Basically the random() function generated non-rounded numbers like 1,23456
Thanks, this was my fix before I saw your example.
<img src="http://s13.postimg.org/mztw3byyf/Star_Fix.png" border="0" />
Also, nice way to load and destroy at start the sprites (I've put them outside the screen, but your solution is better)