After "Insert row" you see empty fields if you have a trigger

I have this trigger:

CREATE TRIGGER `tbl1_before_insert` BEFORE INSERT ON `tbl1` FOR EACH ROW BEGIN
SET NEW.col_id = custom_id();
END

When I add a row to tbl1, first time after I hit enter key or click "Post" button, I see blank fields or NULL fields(first row in attachment), I have to refresh to see the proper values(second row in attachment).