hi Raphael,
The problem that is occuring here is that you are using the decimals in the quantity of the PR.
Let us assume you are using the UoM EA
Go to tcode CUNI
click on unit of measure
Select the UoM as EA and click details button
You can see the decimal rounding place.
It will be some non zero value. Make it zero to prevvent rounding of the quantity in UoM
Regards
Vivek Singh