However; if I made any attempt to resolve it at the time, if they were in any way inconsiderate at the time... then I would feel no remorse just forgetting about it. It's not your responsibility to ensure they do their job - especially after telling them how to do it, or if they are failing to your job.
In short, your moral obligation is dependent how much you are responsible for the issue. You didn't cause the problem and after you attempted to resolve it. That combined with the original responsibility being with them... you are most certainly not obligated to instill a cost upon yourself for their benefit.