To reproduce:

 public Form1()
 {
     InitializeComponent();

     this.radRibbonBar1.CollapseRibbonOnTabDoubleClick = false;
 }

Workaround:

if (this.radRibbonBar1.CommandTabs.Count > 0)
{
    this.radRibbonBar1.CollapseRibbonOnTabDoubleClick = false;
}