Strange SQL Statement Behavior

I have a simple SQL statement (executing on a SQL Server upgraded from 2000 to 2008 R2):

SELECT TOP (1)
    DocNox = CONVERT(integer, SUBSTRING(DocNo, 2, LEN(DocNo)-1)
FROM Tbl1
WHERE
    Fld1 = 19 
    AND Fld2 = 1
    AND Fld3 = 1 
    AND DocNo NOT LIKE '%-%'
ORDER BY
    CONVERT(integer, SUBSTRING(DocNo, 2, LEN(DocNo)-1) DESC;

Sample data (Serial is an IDENTITY column)

Serial   DocNo    Fld1   Fld2   Fld3
211      A1       19     1      1
212      A2       19     1      1
213      A003     19     1      1
214      X1-C1-1  20     1      1

Executing the query produces this error message:

Error converting nvarchar value '1-C1-1' to a column of data type int.

This is unexpected because the row containing that value ought to be filtered out by the WHERE clause before the conversion in the SELECT and/or ORDER BY clauses.

I have noticed that the following changes prevent the error occurring:

• Changing the condition WHERE Fld1 = 19
• Copying the data to another table with the same structure
• Removing the TOP (1)
• Removing the ORDER BY
• Changing the ORDER BY to a different column (e.g. Serial)

But the error still occurs in the following circumstances:

• Importing the whole table to another database
• Running the same statement against a different database with the same data

I also made a change to the statistics that prevented the error but I cannot remember exactly what I did.

Can any one explain what is happening here?