ADDING CUTAWAY SHORTENS .MOV by 1 SECOND WHY??

Another question, I am having an issue that I've created a cutaway of several pics on a frame that I created for slideshow, the main frame is timed out at 30 seconds, and I created 6 cutaways to the main... timed at 4.2 seconds each... when I put the .mov file to create the cutaway on the main, I strech all out, have even tried using "inspector" to set the cutaway for 30 seconds to match the main slide. I've actually been able to get it to strech to 30 seconds, the cutaway that is, however when I go to export using quick time to create an mp4, i-movie crashes... I figured it out that if I didn't strech the .mov file to match the 30 on the main slide, it exports fine... only problem is main slide comes up and is missing pic in pic for like a second. Can anyone tell me what the **** this is about??