Steps to reproduce:

1. Go to Items (or Item Prototypes)
2. Click Create item
3. Switch to Preprocessing tab
4. Select any of the following steps: Regular expression, XML Xpath, Prometheus pattern, In range
5. Custom on fail checkbox is enabled and unchecked - EXPECTED
   
6. Select step "Check for not supported value"
7. Custom on fail checkbox is disabled and checked - EXPECTED
   
8. Select any of steps from #4
9. Custom on fail checkbox is disabled and checked - NOT EXPECTED