How to prevent non-catalog lines from grouping due to identical description?

Some requesters will create a requisition with several lines that have the same description.

Then, the user will check the "negotiated" box and, once the PR is approved, the system will auto create a PO.

As the description is the same, the system will group the requisition lines, will add the quantities and will randomly take a unit price from one of the original requisition lines.

Therefore, the total on the PO will never match the total on the PR.

We have recommended the users to add a number a the end of the description to avoid this "functionality" but they keep forgetting to do it. Example: