[dnanian]

There are a lot of posts here dealing with this exact issue, Armand: it's the way HFS+ handles deleted space, and there's really nothing we can do to make it not expand.

To recover the space, you can use hdiutil. Open Terminal, type:

hdiutil compact

with a space after it, then drag in the (unmounted) image file. Press Return at the end, and it'll recover the free space.