I just found this out today and it's astonishing that it hasn't been 'fixed' already.

When you derive a product although all the files and items you need to display that product in IMvu are included in the *.cfl file, IMvu itself will insist on downloading the files you derived from as well; redecorate the castle walls and upload that to the catalogue, IMvu will download that and the version of the castle you derived from even though it has no physical influence over the product you made.

The purpose of this post is to make you aware of what this means, the file size of your items balloon out of all proportions to what's there because all the products in the derivation chain get added to your final product (again, even though they have absolutely nothing to do with what you did to your version of the products). Example... furniture items can be derived from IMvu's bar, right? Well this isn't what I call an 'originating item'; it's not the 'root' item or 'start' of the derivable chain for that product type. i.e.;

Instead of this

imvuBar > my tombstone

You have this;

buckstars coffee shop > corel reef > original two room shell > Bar (light Brown) > my tombstone

And that essentially means that when "my tombstone" is loading in, IMvu is also loading in buckstars, the corel reef, original two room shell and the bar! That's a lot of wasted data and download bandwidth being used up on something that does nothing. In other words; this is one big problem for people creating new furniture meshes and furniture rooms because the sample files are already several 'generations' up from the original 'root' product; a simple 60KB chair is now 1500KB; have a 1500KB file with some music and you may find that it's over the 2MB limit set in place by IMvu themselves!

The moral of this is to try and check the derivation chain on a product before you start it, especially if you're thinking of meshing. *shakes head in astonishment at IMvu's ineptitude missing such a fundamentally bad decision they should have had the foresight to have seen*