GUI.SelectionGrid elements size problem

Sorry for my bad english, i used google translate:) I have a problem with GUI.SelectionGrid:

 _currentElementIndex = GUI.SelectionGrid (
                  drawRect, _currentElementIndex, new string [scores.Count], 1, _guiRowStyle?? GUI.skin.button);

Here drawRect.height = 51 * new string [scores.Count] Suppose, when one item is drawn, it looks like a 51 pixel. When the 20 items is drawn, the first element is 48 pixels. All other elements are shifted to these 3 pixels higher. Why is this happening? My SelectionGrid embedded in Gui.BeginScrollView, if it can help.