Thank-you all for your kind comments and feedback.
I am sorry that a few of you did have some trouble trying to get the code running on your servers. I also apologize for not having the time during the day to reply to all who took the time out to comment (had a busy day at home and at office today).
What fascinated me the most about this was that it taught me a little something about constraints and how SQL Server uses them (i.e. the use of the constraint made SQL look for the index, which was disabled).
To all those who read the question and took the time to attempt it - a very big thank-you from me. To all those who learnt something new, SQL is magical and this question is even more motivation to learn more about it!
Have a wonderful weekend ahead!