Hi Mark and Luis!
Unfortunately I failed to replicate the issue which you mentioned. But there are some tricks with this module.
1 - First of all you should enter right "U.S.P.S. API server URL" , testing or production. It depends on your account type
http://awesomescreenshot.com/00f2ie2j14
2 - Test rates calculation
http://awesomescreenshot.com/0032ie5z86
3 - If USPS module can find new shipping methods(which are not included in our USPS module) in the response they will be added to database as disabled methods. You should enable them
http://awesomescreenshot.com/0da2ie5vb4
4 - Go to checkout page and test it.
http://awesomescreenshot.com/05e2ie8t63
Sorry for this inconvenience, we will add all this new USPS shipping methods as enabled methods in the next version of "USPS" module.