this.comments.Value += row["messages"].ToString();
this.comments.Value = Environment.NewLine;
Perhaps if the second line was
also "+=" rather than "=" it would make a difference?
BTW: it would make a lot of sense to replace the
this.comments.Value
with a StringBuilder - particularly if there are expected to be a lot of rows - remember that strings are immutable in C# so you create a new string every time you concatenate two of them.