When-validate-item fail, should stay in the error field... but that is not my case

I have a simple form with one window.  The window/canvase only have 3 fields only.  They  cust_class, start_date, end_date.  It is in Tabular.

I have a When-validate-item on both start_date and end_date to make sure the end_date is not before the start_date.  When the when-validate-item failed on start_date, it pop up an error message as expected.  Then I click OK.  The cursor will stay in the start_date field.  However, that is not the case for end_date. 

When-validate-item failed on end_date, it pop up error message as expected.  Then I click OK.  The cursor move to next row!