Validation on Person National Id>Cancel button on the National Id section does not work

Summary:

Validation Rule on Person object > Validation on Person National Identifier > Cancel button on the National Identifier section does not work

Content (please ensure you mask any confidential information):

Hello All,

We have developed an auto complete rule on the business object Person so that the user cannot delete National Identifier of an employee if it has only one NID : Basically, we are looping on the Person National Identifier, for each interation we are incrementing a counter. If this counter is equal to 0, we are showing an error message to the user (This is working)

However, after clicking on the OK button of the error message and when the user clicks on the Cancel button in the National Identifier section, the section is not being closed, it is like the Cancel button does not work. Any idea why ?