To reproduce:

Use Nikolay's project from this post: http://www.telerik.com/forums/scrolling-using-wraplayoutpanel . Run it and click just below the scrollbar  thumb, it will now move to the bottom. Now click above it and it will move to the top. At some cases (every second click or so) you will notice that the thumb is moving but the controls inside do not.

Workaround:

Subscribe to the ValueChanged event of the scrollbar and invoke PerformLayout of the PanelContainer:

this.radScrollablePanel1.VerticalScrollbar.ValueChanged += VerticalScrollbar_ValueChanged;

void VerticalScrollbar_ValueChanged(object sender, EventArgs e)
{
    this.radScrollablePanel1.PanelContainer.PerformLayout();
}