Tree animation issues.

Firstly, I would like to thank for this great framework, that I'm using in my web application.
I'm using tree view and everything is OK till I add expand animation to tree. I'm adding animation via css like this:

$v-tree-expand-animation-enabled: true;

And this is how I added Tree view to my layout:

VerticalLayout layout = new VerticalLayout();
setCompositionRoot(layout);
layout.setWidth("100%");
this.tree = new Tree();
layout.addComponent(tree);
for (int i = 0; i < 5; i++)
{
StringBuilder sb = new StringBuilder();
sb.append("grand_").append(i);
String grand = sb.toString();
tree.addItem(grand);
for (int j = 0; j < 6; j++)
{
StringBuilder sb2 = new StringBuilder();
sb2.append("parent_").append(j).append("_").append(i);
String parent = sb2.toString();
tree.addItem(parent);
tree.setParent(parent, grand);
for (int k = 0; k < 7; k++)
{
StringBuilder sb3 = new StringBuilder();
sb3.append("child_").append(k).append("_").append(j).append("_").append(i);
String child = sb3.toString();
tree.addItem(child);
tree.setParent(child, parent);
tree.setChildrenAllowed(child, false);
}
}
}

The animation works but when expanding or collapsing items a problem appears. The problem is that tree items are over drawed on each other when collapsing items and the expand animation is not looked nicely. I've posted this question in StackOverflow here, but didn't get an answer.

I'm using Vaadin 7.6.2 version, theme - valo theme, sevlet container - apache-tomee-plus-1.7.2, client's OS - Windows 7, client's browser - Google Chrome - 48.0.2564.116.(I'm sorry for my English, if I have grammar mistakes)