Please refer to the attached gif file.

Workaround: adjust manually the RadRibbonBarGroup.Margin when the expanded state is changed:

public Form1()
{
    InitializeComponent();
    this.radRibbonBar1.ExpandedStateChanged += radRibbonBar1_ExpandedStateChanged;
    radRibbonBar1.Expanded = false;
}

private void radRibbonBar1_ExpandedStateChanged(object sender, EventArgs e)
{
    if (this.radRibbonBar1.Expanded)
    {
        AdjustMargin(0);
    }
    else
    {
        AdjustMargin(-10);
    }
}

private void AdjustMargin(int top)
{
    foreach (RibbonTab tab in this.radRibbonBar1.CommandTabs)
    {
        foreach (RadRibbonBarGroup group in tab.Items)
        {
            group.Margin = new Padding(0, top, 0, 0);
        }
    }
}