Hi Marcelo
MRP will not consider the production order tolerance during the net requirements calculation. If the sales order requirement is bigger than the stock, a new planned order will be generated.
A solution to this issue is to use BAdI MD_CHANGE_MRP_DATA to make your own logic and make the sales order not relevant to MRP.
See the following blog post for an example of this BAdI:
Making an element not relevant to MRP or MD04 using BAdI MD_CHANGE_MRP_DATA
BR
Caetano