This article discusses an issue, and provides a solution, with Final Cut Pro while using the JKL feature at less than 1x speed.

Symptom

While using the JKL feature in Final Cut Pro 1.2.1 or 1.2.5, and holding down the K and L keys on the keyboard, I tried to mark an IN point with the I key. Nothing happens.

Solution

With Final Cut Pro 1.2.1 and 1.2.5, you can navigate a clip or sequence at less than 1x speed by holding down the K key, and holding down the J key for reverse or the L key for forward. While using this function, you may be unable to mark an IN or OUT point using the I and O keys on the keyboard. Instead, use the / and * keys on the numeric keypad to set an IN or OUT point.