I will demonstrate this as an example for better explanation:

We have item1 belong to sales agreement SA01 with price = 11

item2 belong to sales agreement SA02 with price = 12

item3 belong to sales agreement SA03 with price = 13

Let say the default price for all 3 released item 1, 2 and 3 is 0 

Current behavior on price simulator: 

add item1 in sales line 1

add item2 in sales line 2

add item3 in sales line 3

 -> this should trigger the sales agreement ID to select SA01 since item1 added as sales line 1 

This will give the preview price for the 3 items as below: 

Item1 preview price = 11

item2 preview price = 0

item 3 preview price = 0 

The expectation is that, when the sales line is added in the price simulator, it should not default any sales agreement id for the remaining lines, then the preview price for the 3 items should be displayed based on each of the sales agreement the items belong to: 

item1 preview price = 11

item2 preview price = 12 

item3 preview price = 13