I have this problem (or maybe I've misunderstood something).
1) Creating link to a Project from a Sale.
2) Relations table in DB gets a new line, with relDef_id = 10, source_table = 11 (project) and destination_table = 13 (sale)
3) Deleting link from the same Sale. Now the link can't be seen on the sale
4) At first it can't be seen at the project.
5) Pressing F5 -> Now the link can be seen again.
6) Restarting SO and the link is again present at the sale.
They are using SO 84 Windows, and the problems accours on several machines. All scripts are deactivated.