1.7.8.0 Shipping cost problem with product virtuel and product classic

[Blawdi]

Hello,

I have a problem with prestashop 1.7.8.0 :

I have a carrier by weight:
0 to 0.2 kg = price 3$

Another carrier by price : 
0 to 80 $ = Price 7.5
81 to XXX = free

I add a product that is 0.19kg
In the cart the right price of the carrier is displayed 3$.
I add a virtual product
The price is 7.5 

The product is virtual why does it change the price?