actionscript 3 - Flash AS3 FileReference.save() not working on Android AIR -

i have following code save movieclip png image:

download_btn.addeventlistener(touchevent.touch_end, function(){     if(currentimage == andy_thumb){         savepicture(movieclip(parent).andy, 'andy');     }     if(currentimage == tilly_thumb){         savepicture(movieclip(parent).tilly, 'tilly');     }     if(currentimage == trunk_thumb){         savepicture(movieclip(parent).trunk, 'trunk');     } });  function savepicture(mc:movieclip, charname:string):void {     var bmd:bitmapdata = new bitmapdata( mc.width, mc.height );     var bounds:rectangle = mc.getbounds(mc);     bmd.draw(mc, new matrix(1,0,0,1,-bounds.left, -bounds.top));      var file:filereference = new filereference();        file = new filereference();      file.save(pngencoder.encode(bmd), charname+'.png');  } 

this works fine when debug on computer. when using tablet, download dialogue box opens, when click "ok" after specifying file location download to, doesn't save file.

any idea's why?

thanks.