If you copy a clip from one sequence and then paste it into another, you may not see a dialog that will adjust the new sequence to the settings of the original clip.

Programs
Final Cut Pro 6.0, 7.0

Solution

Copy the clip from the Browser and then paste it into the timeline of the new sequence. Following these steps will bring up the dialog offering to adjust the sequence. If you have already pasted the clips directly from another sequence, you can adjust the new sequence manually to fit the clips.