Can't get leafs check value with progressive render

What steps will reproduce the problem?
Load a tree using checkbox plugin via JSON and ajax, with a depth of 4 levels, 
using progressive_render

What is the expected output? What do you see instead?
EXPECTED: All parent checks should appear properly checked the way leaf are 
checked.
REALITY: While leaf nodes are not shown(opened) parent nodes won´t appear 
checked (or undetermined state if applies)

What version of the product are you using? On what browser?
Version: 1.0rc2
Browser: IE8

Please provide any additional information below.
I solved partially this issue establishing the proper class to any node in my 
code. I check if all child nodes of a node are checked, and then apply the 
jstree-checked or jstree-undetermined class.
The current problem is when I have a parent node with class jstree-undetermined 
and I don't have opened leaf nodes yet, I can´t read leaf check values until I 
open this branch.

Original issue reported on code.google.com by mr.k...@gmail.com on 12 Jan 2011 at 11:45

OdinaSpb / jstree

Can't get leafs check value with progressive render #864