I do see this problem here when the MultiColumnCombobox is in DropDownList mode. You could workaround this problem by handling the MultiColumnCombobox.PopupContainer''s BeforePopup event as shown below :
this.multiColumnComboBox1.PopupContainer.BeforePopup += new CancelEventHandler(PopupContainer_BeforePopup);
private void PopupContainer_BeforePopup(object sender, CancelEventArgs args)
if (Control.MouseButtons == MouseButtons.Right)
args.Cancel = true;
I have attached a complete sample
that demonstrates the above mentioned workaround. Please refer to it and let me know if you need further assistance.