That is because it is not valid: it is not allowed to nest interactive content (such as buttons) within a button. This means that your big button must not be a button element.
Try making your big button a span element / div element with display: inline-block; to simulate a similar effect. Of course, you might also want to add some custom logic to make it feel a button (hover / focus / tabindex et cetera), but that depends on your needs.
See also this answer for an overview what is not allowed to be nested within a button: Can I nest button inside another button?