When you use ArcGIS' Project tool it creates a new featureclass. This is awesome, unless the featureclass you projected had been related to twenty-some tables. All of those relationships still point to the original featureclass, but not the new one, as described in this ESRI article. So, does anyone know if there is a good way to point an existing relationship class at a different featureclass without deleting the relationship class?
Short of mocking with the gdb tables (which is an unsupported option), you have to delete the relationship classes and recreate them. You can do so manually or with a script, but the delete/create cycle still needs to happen.