philx , i really don't get it , maybe the problem in your mobile that shift the sprite position,
also if you are using android you can show the touch input from : sitting >> devolopers (or something like this) then click on the box that says : show touches , and maybe you can see the shift in the screen...
also maybe its from your finger is too fat or maybe the origin point of the sprite isn't on the center or or or .. there are many reason that cause the same problem.
as to make sure i have tried the demo on the pc and it works fine when i re-downloaded the capx file and played , the link that has the demo is broken from the server i don't know the reason :(
anyway try these steps and i hope it fix it :)