datagridviewcomboboxcolumn 有时选择下拉时，背景色为什么变了颜色

我在下拉控件中加了此事件，目地是当我在第一个datagridviewcomboboxcolumn中选择某一个指定值 的时候，第二个datagridviewcomboboxcolumn 会自动选择第一个值，但两个框选来选去的时候 ，会出现，
如图的BUG http://hi.csdn.net/space-4312833-do-album-picid-914548-goto-down.html
，不知道怎么解决，请各们有劳了，谢谢！

C# code

        private void dgvVar_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)        {            if (this.dgvVar.CurrentCell != null && this.dgvVar.CurrentCell.OwningColumn.Name == "colVarType")            {                ComboBox cb = e.Control as ComboBox;                cb.SelectedIndexChanged += new EventHandler(FormIntelligenceDocument_SelectedIndexChanged);            }        }        void FormIntelligenceDocument_SelectedIndexChanged(object sender, EventArgs e)        {            ComboBox cb = sender as ComboBox;            if (cb != null)            {                if (cb.Text == "其它字典")                    this.dgvVar.CurrentRow.Cells["colVarZD"].Value = this._VarTypeZD.Rows[0]["Code"];                else                    this.dgvVar.CurrentRow.Cells["colVarZD"].Value = null;                ////让变量类型失去焦点                //this.dgvVar.EndEdit();                //(sender as ComboBox).SelectedIndexChanged -= new EventHandler(FormIntelligenceDocument_SelectedIndexChanged);            }        }

[解决办法]
楼主，你把每个可能设置背景色的地方，都检查一下：是不是人为设成了黑色！
BackgroundColor 、AlternatingRowsDefaultCellStyle 、ColumnHeadersBorderStyle 、ColumnHeadersDefaultCellStyle 、DefaultCellStyle
[解决办法]
估计是某个属性设置问题
[解决办法]

C# code

       private void dgvVar_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)        {cb.SelectedIndexChanged -= new EventHandler(FormIntelligenceDocument_SelectedIndexChanged);            if (this.dgvVar.CurrentCell != null && this.dgvVar.CurrentCell.OwningColumn.Name == "colVarType")            {                ComboBox cb = e.Control as ComboBox;                cb.SelectedIndexChanged += new EventHandler(FormIntelligenceDocument_SelectedIndexChanged);            }        }
[解决办法]
探讨


就设置了这两个属性    
        dgvCbx.DisplayStyle = DataGridViewComboBoxDisplayStyle.Nothing;
        dgvCbx.FlatStyle = FlatStyle.Popup;