Flex SDK 3.5 builds bigger swfs

I have an application which is almost entirely in actionscript.

When I build it using Flex SDK 3.5 its size is roughly 378 KB,

While Fle开发者_运维问答x SDK 3.0 outputs a swf with roughly 355 KB.

What could the reason be?

I think it's because more code has been
added to the existing classes.