Jquery Dialog doesn't drag on android browsers

My jquery dialogs doesn't drag on android browsers but drags well on firefox and Chrome on my windows xp computer: Any idea ?

On my android tablette, the windows aren't draggable it stays bloqued, i don't know why.

You can test it there

http://nicolash.org/exercice18Modificationobjet/

It doesn't work there also :

http://jqueryui.com/dialog/

I can see the mouse cursor change, but its impossible to drag. PLease help thank you!