To Reproduce:

Add a RadDropDownButton on a form, then create a RadMenuItem and a RadTrackBarElement element. Add the trackbar to the children`s collection of the menu item, then add the menu item to the items`s collection of the RadDropDownButton element. Application freezes when you move the drag ball and it gets close to the end of the trackbar.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        RadTrackBarElement trackBar = new RadTrackBarElement();
        //trackBar.StretchHorizontally = false;

        RadMenuItem menuItemTrackBar = new RadMenuItem();
        menuItemTrackBar.Children.Add(trackBar);
        this.radDropDownButton1.Items.Add(menuItemTrackBar);
    }
}

Workaround:

Set StretchHorizontally property of the trackbar to False.

trackBar.StretchHorizontally = false;