Steps to reproduce:
1) Add RadGridView control
2) Use GridViewDecimalColumn:

        DataTable customDataTable = new DataTable();
        sampleDataTable.Columns.Add("Column name", typeof(double));

3) Set the right-to-left property of the control to true:

        this.radGridView1.RightToLeft = System.Windows.Forms.RightToLeft.Yes;

4) Re-size the form manually until horizontal scroll-bar appears and you will notice that the left border is missing

Expected result: the left border of the GridRowHeaderCellElement is visible
Actual result: the left border of the GridRowHeaderCellElement is missing

Workaround:
this.radGridView1.ViewCellFormatting +=new CellFormattingEventHandler(radGridView1_ViewCellFormatting);
 
void radGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
{
    if (e.CellElement is GridRowHeaderCellElement)
    {
        e.CellElement.BorderLeftWidth = 3;
    }
}