Excel '03 Data Filter puzzle

I'm using Excel '03 and I have two columns with data, A & B. Column A holds
the name of a letter and Column B stores the body of the letter. When I
apply a Data Filter to these two columns, it isn't working. For instance, I
have about 30 letters that have the word "seven" in them, but when I do a
"Custom - Contains - seven" in Excel '03, it only shows 2 items.

I had someone who has Excel '07 try it, and it shows all 30 items. There
are approximately 607 letters/rows on this sheet.

Does anyone have any idea what the issue is?

Thanks!