Program-crashing tweens

I made a program in AS3 that creates a lot of tweens, over and over again. It would seem to work fine and then crash suddenly, at random places with no discernible pattern. The program would just stop dead, and I’d have to close the swf.

When you create a new tween, you don’t necessarily need to assign it to a variable, right? You can just have new Tween(properties, etc.); on it’s own line and it’ll carry itself out. So that’s what I did. Yet the only way I could fix the program was by assigning all the tweens to variables like with var t:Tween = new Tween(yada yada yada). It didn’t crash after that.

Why does this happen? Thoughts? Explanations?