datagridview reverts changes when using the InsertCopy-Method?

[rilkar]

Upon commiting changes to a row the following method is executed:

...
// Commit the value to another function and read back a properly formatted string. E.g. if the value was 123 it will now be 123.00
dataGridView1[e.ColumnIndex, e.RowIndex].Value = Manager.UpdateTransaction(newRow, e.ColumnIndex, dataGridView1[e.ColumnIndex, e.RowIndex].Value.ToString());
...
// the value of the cell dataGridView1[3,e.RowIndex+1].Value is 123.00
// delta is negative in the next command
dataGridView1.Rows.InsertCopy(e.RowIndex, e.RowIndex + delta);
// the previous row is now located 1 row further dataGridView1[3,e.RowIndex+1].Value

however is now 123 instead of 123.00

Why is the string value being reset from 123.00 to 123? It doesn't make any sense to me...