Create a Write document.
Create a Text Table.
Place the cursor in the text table.
Run the following macro



Sub tbl_border_onerow 'blue
   Dim oSels,oTables,oCells
   Dim oVC
   oSels = ThisComponent.getCurrentController().getSelection()
   oVC = ThisComponent.getCurrentController().getViewCursor()   
   'oVC.cell.BottomBorder = MakeCellBorderLine( RGB(0,0,255), 150, 150, 100)   
     
   Dim oBorderLine
   oBorderLine = oVC.cell.BottomBorder
   With oBorderLine
      .Color = RGB(0,0,255)
      .InnerLineWidth = 150
      .OuterLineWidth = 150
      .LineDistance = 100
   End With
   oVC.cell.BottomBorder = oBorderLine
End sub


You now have a double blue line as the bottom line in the cell with the cursor.
Now, save the document, close the document, and open the document. The double
line is gone (there is no line). 

If you change the LineDistance from 100 to 0, then I observe no problems.