SQL Select And Logical OR

I have a query. on my search page i have a number of textboxes e.g. title, subtitle, ISBN where users can enter a search string and when they click on a button the data is displayed in the gridview below.

my query seems to be bringing up the right records but with some additional records into the gridview. I have tried the same query within the SQL server management studio and it brings back two records like indicated but within my aspx page it brings back 6 additional records that have no relevance to the query. Im quite baffled as to why this is happening and i have debugged but nothing comes to light.

my code in my aspx page is as follows:

public void BindData()
{
String _BookID = TxtBookID.Text;
String _Title = TxtTitle.Text;
String _Subtitle = TxtSubtitle.Text;
String _ISBN = TxtISBN.Text;
String AuthorFName = TxtForename.Text;
String AuthorLName = TxtSurname.Text;

SqlDataAdapter ad = new SqlDataAdapter("SELECT Book_ID, Book_ID_Internal AS [Book Internal ID], Title, Subtitle, ISBN, Edition, Publication_Date AS [Published Date] FROM Book WHERE Book_ID_Internal = '" + _BookID + "' OR Title = '" + _Title + "' OR Subtitle = '" + _Subtitle + "'", conn);
DataSet ds = new DataSet();
ad.Fill(ds, "Book");
if (ds.Tables[0].Rows.Count == 0)
{
//if there are no rows returned-state in the grid
ds.Tables[0].Rows.Add(ds.Tables[0].NewRow());
GridView1.DataSource = ds;
GridView1.DataBind();
int columncount = GridView1.Rows[0].Cells.Count;
GridView1.Rows[0].Cells.Clear();
GridView1.Rows[0].Cells.Add(new TableCell());
GridView1.Rows[0].Cells[0].ColumnSpan = columncount;
GridView1.Rows[0].Cells[0].Font.Italic = true;
GridView1.Rows[0].Cells[0].Text = "No Records Found";
}
else
{
GridView1.DataSource = ds;
GridView1.DataBind();
}
}

if i input the same query into SQL management studio:

SELECT * FROM Book WHERE Book_ID_Internal = 'ITD 450' OR Title = 'HTML 4.0'

it returns two records which is correct.

Can anyone see where i am going wrong?