Another workaround is to set the NullValue of the column to the desired text. In a project of mine I have a DataGridView where the user can add rows manually. The text for the button didn't appear and nothing seemed to work. I then remembered that there is always a NullValue property and after I set this, the text appeared on the button ;)
DataGridViewCellStyle8.NullValue = "Some Text"
Me.AddStillstand.DefaultCellStyle = DataGridViewCellStyle8
Me.AddStillstand.HeaderText = ""
Me.AddStillstand.Text = "Some Text"
Just in case someone else is having a similar issue ;)