I found a lot of problems in the module and, looking to the code, a lot of things seems very strange/understandable for me :

in uc_worldquote_match_weight() :

$max_amount = $worldquote->max_amount * constant(strtoupper($units) .'_TO_KG');

Damn strange, you want to conver the maximum amount price into Kilogram ???!!!

if (($max_amount) && ($pkgweight > $max_amount)){

And then, you want to compare the package weight with an amount ?

I don't understand this lines of code, for me, the maximum order amount price, is the maximum order price fot which all order with a superior amount is shipped for free.

I think lots of problems come from this function, I have a lot of difficulties to understand why because I can't trace anything (my drupal_set_message() or print, just show.... nothing, I don't understand why).

I will try to post a patch if I found all problems, but with my trace problem, it will be really hard