Steps to reproduce:

• Open the item form and fill in all required fields.
• Add a preprocessing step of type "Regular expression" and fill in the "Pattern" and "Output" fields. Leave the "Custom on fail" option untouched.
• Save the item.
• Reopen the just-saved item and go to the "Preprocessing" tab.

Result:
The "Custom on fail" option is enabled.

Expected:
The "Custom on fail" option should remain unset (disabled) if it was not explicitly selected.