Cinema Tools 1.0 is unable to handle keynumbers that "roll over" from 9999 to 0000, a convention common with some brands of film (such as Fuji), although it will not happen with Kodak film.
Symptom
Cinema Tools adds a fifth digit to the keynumber instead of rolling over to 0000.
Solution
Upgrade to Final Cut Pro 4.0, which includes Cinema Tools 2.0.