Revert back to passing in array values. We can indexBy in JS

assets/js/admin/settings-views-html-settings-tax.js

@@ -23,7 +23,7 @@
 			WCTaxTableModelConstructor = Backbone.Model.extend({
 				changes : {},
 				setRateAttribute : function( rateID, attribute, value ) {
-					var rates = this.get( 'rates' );
+					var rates = _.indexBy( this.get( 'rates' ), 'tax_rate_id' );
 
 					if ( rates[ rateID ][ attribute ] !== value ) {
 						rates[ rateID ][ attribute ] = value;

includes/admin/settings/class-wc-settings-tax.php

@@ -157,7 +157,7 @@ class WC_Settings_Tax extends WC_Settings_Page {
 		wp_localize_script( 'wc-settings-tax', 'htmlSettingsTaxLocalizeScript', array(
 			'current_class' => $current_class,
 			'base_url'      => $base_url,
-			'rates'         => $rates,
+			'rates'         => array_values( $rates ),
 			'page'          => ! empty( $_GET['p'] ) ? absint( $_GET['p'] ) : 1,
 			'limit'         => 100,
 			'countries'     => $countries,