Autofill popup list box should have the same width as its input field's width. If the submitted input text is longer, it will be truncated to fit in the input field's width
Try type some long text in the "Last name" input box, Say "abcd abcd abcd abcd abcd abcd". then click "Submit". Open the file again, and type the first letter "a", the form autofill pop-up should show up now with the width the same as the width of the input field, and the text "abcd abcd abcd abcd abcd abcd" got truncated to fit in.
Try type the following text into the "First name" and "Last name".