Here's an interesting occasional bug in FCP:
I had two clips and their associated audio tracks highlighted. Then I hit Shift+Delete to perform a ripple delete. But one unassociated audio track refused to budge. You can see the result in the two following images.
Before the Ripple Delete
After the Ripple Delete
A restart of FCP fixed it which goes to show that something as complex as FCP can get confused sometimes.
Always make sure you set your auto-saves to a different drive than your project drive (preferably one with Time Machine going) and don't be reluctant to save and restart FCP when things get strange.
(the stills were pulled from a video my assistant took with his little portable camera, it's interesting to see the convex curves in the stills even though the editing monitor is a flat LCD, due to the lens on his camera)