I found an interesting article at ScottGMorgan.com. He apparently ran into an issue where garbage collection was killing his tweens prematurely sometimes, but sometimes it would not.

To sum up his article… If you use some sort of loop with a temporary variable that continually gets overwritten by the following iteration, the garbage collection cycle will recognize these unassigned tweens and remove them before they can complete.

Good article Scott.

Read the full article here:

http://www.scottgmorgan.com/blog/index.php/2007/11/18/as3-garbage-collection-the-reason-your-tweens-are-ending-early/