Autocomplete rule not working

Summary:

I have created a rule with business object: Job requisition- where requirement is throwing error message when there is business unit and legal employer mismatch.

Content (required):

I have created a rule with business object: Job requisition- where requirement is throwing error message when there is business unit and legal employer mismatch.

I have created the rule, but that rule is not working for either field validation or Object Validation(which throws error and won't let user to save). but it is working on field modification (which throws warning message and user can save and close).

Just wanted to know, how the same rule configuration is working for Feild modification but not for Object Validation/Feild Validation.