Hello Abdessamad ,
As mentioned by Ganesh, Cube consider all dimension characteristics as well as data package characteristics (based on request id) as key field. Info cube always works on aggregation summation mode so it never overwrites data.
If you are having all correct data through second load then delete your previous loaded request from info cube.
If you would like to perform some more tests then do compression on info cube request. It will merge all request id and one request id and then you can check behaviors of data into info cube. But once requests are compressed you are not able to delete data request by request.
Hope it helps.
Regards,
Sangita