Your code is nearly working.
But there is one javascript issue, a global variable pollution, which prevents it from working.
fixed your jsfiddle: http://jsfiddle.net/63tGP/3/
it fixed
self = this;
to
var self = this;
self = this;
is same as window.self = this;
the result is, at the end, the self in your addTask() always points to the last testModel.
2
solved Knockout bootstrap modal issue