False duplicate relationship
In our case, we use the description to define the job title so we want to have the history of the different job title over time. I see no reason why we couldn't have multiple inactive employer relationship with the same organisation and only one active at a time.
It's not possible to create 2 relationship of the same type with the same contacts even if the other one is disabled.
On the other hand, if we have a start and/or end date on the relationship, the checkDuplicateRelationship doesn't consider it to be a duplicate.
If we remove the start date from the inactive relationship, there is no warning so after all it's possible to do what we want but with some unnecessary steps.