scrollbar keeps on scrolling down in jstree

I have a set of data being displayed as a tree by the help of jstree plugin and jquery.

The data shows up perfectly in the tree structure. On expanding the last node in the tree the scrollbar appears on the right side of the div block.

Problem: However if I navigate within the tree with the mouse over the scrollbar, the scrollbar keeps on scrolling down and does not go up.

I am at wits end what could the reason be. I am using a Mozilla Firefox browser.

Please help.

Sample Code below:

css:

.myScrollableBlock {
display:block;
height:170px;
overflow:auto;
}

.jsp:

<div id="myTreeDiv" class="myScrollableBlock">
</div>

.js:

$('div#myTreeDiv').jstree({
// jsTree plugins
    ...
    ...
    ...
});