First letter always cap

Hello, good afternoon. First, congratulations for the plugin. I use it on all websites. I am using the code in functions.php of my theme.

add_filter( 'wpcf7_posted_data', 'your_wpcf7_posted_data' );

function your_wpcf7_posted_data( $posted_data ) {
	$name_fields = array( 'first-name' );

	foreach ( $name_fields as $field )
		$posted_data[$field] = ucwords( $posted_data[$field] );

	return $posted_data;
}

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As often as it works and sometimes not. There any way to ensure the operation?

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