Setting the TopRowIndex seems to home the scrollbars for me in your sample. Here is the code I used. I modified the code that was setting the Position to zero as the previous code seemed to not set the focus to the grid in some cases, but that did not affect the scrollbar for me.
BindingManagerBase bmb = this.BindingContext[this.edbgMain.DataSource, this.edbgMain.DataMember];
bmb.Position = 0;
this.edbgMain.TopRowIndex = this.edbgMain.Model.Rows.HeaderCount + 1;
this.edbgMain.EndUpdate();
this.edbgMain.CellClick += new GridCellClickEventHandler(edbgMain_CellClick);
What steps do I take to see the problem in the sample?