Thank you for writing.
If I have understood your case correctly, your last RadListBoxItem is close to the bottom border of your RadListBox and you get both the vertical and the horizontal scrollbars when width of RadListBox is decreased. Generally, this behavior is correct, but if you really want to hide the horizontal scrollbar, you can do it as it is shown below:
.radListBox1.ListBoxElement.ScrollLayoutPanel.HorizontalScrollState = Telerik.WinControls.UI.ScrollState.AlwaysHide;
I hope this helps.
the Telerik team
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