Steps to reproduce:

1. Create a new icon mapping
   Example:
   Result works as expected: 
   
2. Change mapping 1 expression:
   
3. After the update, the Mapping will behave as expected (first mapping doesn't match expression, second mapping matches the expression). Both Elements are correctly mapped:
   
4. Revert the mapping 1 expression back to the original (in this example back to "Core") and update. The Mapping will not work. The Host element with the "Type (Full details)" Inventory field set to "Core" is not updated:
   

Even if we reorder the mappings it doesn't work. 
But if I edit the second mapping and updating the change is applied.