Oracle Forms

Hi Everyone, I have an item in my form called :BLOCK.ITEM_1 with a lov item_lov but with VALIDATE_FROM_LIST property Set to 'NO'
However in When validate Item of :BLOCK.ITEM_1 based on some conditions, I want to force validate from list.
In when-validate-item of the form, I had put this simple code

IF Some_condition Then
message('In condition******************');
SET_ITEM_PROPERTY('BLOCK.ITEM_1' ,VALIDATE_FROM_LIST,PROPERTY_TRUE);
END IF;

However, nothing is happening despite the fact that my message showed up, the item is not forcing this validation. Please advice, am I doing something wrong here or my set_item_property is not right?

Thanks.