After some searches I never found any solution for this. My Magento version is the last, 188.8.131.52 but since first that this problem remains!
Well, this error isn’t just in shipping calculation, this error happens at product tax calculation!
I have a product with price: €7.98 (inc tax).
The tax is configured well and is 21% (yes, here is Portugal is really bad), so, assuming this, the tax fee must be €1.68
Yes, correct, must be but it not be! The Magento assumes €1.38!!!!!!
This is an error or what? The consequence is really annoying, with wrong shipping calculation…
Please, help this pour soul, I tried many configurations but I think this is really a core mistake.