Music Video with transitions problems

When you add the transition do you get a dialog box asking if you want to adjust the timeline? If you don't have enough overlapping video you'll get this box. It's offering to overlap the two clips to create the transition. But as it warns, it will change the length of the timeline, and of course throw everything out of sync. Don't ever say yes to it unless you know sync doesn't matter. Perhaps there's a checkbox to never ask again and you clicked it? I don't remember.