Scratch

I'm new to Scratch, though not to programming, and my computer is fast and runs Adobe CS4 software etc with no problems.
I've read in the forum that correct code sometimes stops working and can be put right by taking it apart and reassembling (why that should make a difference is a mystery to me but I had sussed that already).
Now to my next problem
When a sprite in scaled up eg to appear to come closer, during the running of a program, using the change size by command, why, when the program is rerun does the sprite start at the new enlarged size? I can't find a way to stop it. Is there another way to achieve the effect without having to use set size to 100% at the start of every program?