Load Tinymce for new textarea can't resize -

i have form have 1 textarea (tinymce onload) , 1 button add new textarea (same id,class)

and start tinymce , first textarea couldn't resizeable ? if had 2 textarea onload tinymce, both of them resizeable !

what's wrong , , how load tinymce dynamic textarea?

function starttiny() { tinymce.init({ }); } starttiny();  function addnewtextarea() { action add new textarea here  starttiny(); }