diff --git a/wp-admin/includes/upgrade.php b/wp-admin/includes/upgrade.php
index 4992ff6e41..59b2ad664a 100644
--- a/wp-admin/includes/upgrade.php
+++ b/wp-admin/includes/upgrade.php
@@ -1057,8 +1057,8 @@ function upgrade_280() {
 		$start = 0;
 		while( $rows = $wpdb->get_results( "SELECT option_name, option_value FROM $wpdb->options ORDER BY option_id LIMIT $start, 20" ) ) {
 			foreach( $rows as $row ) {
-				$value = $row->option_value;
-				if ( !@unserialize( $value ) )
+				$value = maybe_unserialize( $row->option_value );
+				if ( $value === $row->option_value )
 					$value = stripslashes( $value );
 				if ( $value !== $row->option_value ) {
 					update_option( $row->option_name, $value );
diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 34efdbd904..dcfe9e3dd9 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -735,12 +735,14 @@ function wp_check_invalid_utf8( $string, $strip = false ) {
  * Encode the Unicode values to be used in the URI.
  *
  * @since 1.5.0
+ * @since 5.8.3 Added the `encode_ascii_characters` parameter.
  *
  * @param string $utf8_string
  * @param int $length Max length of the string
+ * @param bool   $encode_ascii_characters Whether to encode ascii characters such as < " '
  * @return string String with Unicode encoded for URI.
  */
-function utf8_uri_encode( $utf8_string, $length = 0 ) {
+function utf8_uri_encode( $utf8_string, $length = 0, $encode_ascii_characters = false ) {
 	$unicode = '';
 	$values = array();
 	$num_octets = 1;
@@ -752,10 +754,14 @@ function utf8_uri_encode( $utf8_string, $length = 0 ) {
 		$value = ord( $utf8_string[ $i ] );
 
 		if ( $value < 128 ) {
-			if ( $length && ( $unicode_length >= $length ) )
+			$char                = chr( $value );
+			$encoded_char        = $encode_ascii_characters ? rawurlencode( $char ) : $char;
+			$encoded_char_length = strlen( $encoded_char );
+			if ( $length && ( $unicode_length + $encoded_char_length ) > $length ) {
 				break;
-			$unicode .= chr($value);
-			$unicode_length++;
+			}
+			$unicode        .= $encoded_char;
+			$unicode_length += $encoded_char_length;
 		} else {
 			if ( count( $values ) == 0 ) $num_octets = ( $value < 224 ) ? 2 : 3;
 
diff --git a/wp-includes/post.php b/wp-includes/post.php
index 01ffc8718f..640ab81e36 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -3524,7 +3524,7 @@ function _truncate_post_slug( $slug, $length = 200 ) {
 		if ( $decoded_slug === $slug )
 			$slug = substr( $slug, 0, $length );
 		else
-			$slug = utf8_uri_encode( $decoded_slug, $length );
+			$slug = utf8_uri_encode( $decoded_slug, $length, true );
 	}
 
 	return rtrim( $slug, '-' );
diff --git a/wp-includes/taxonomy.php b/wp-includes/taxonomy.php
index ce6da2d0ff..1fb77662c7 100644
--- a/wp-includes/taxonomy.php
+++ b/wp-includes/taxonomy.php
@@ -818,7 +818,11 @@ class WP_Tax_Query {
 			return;
 		}
 
-		$query['terms'] = array_unique( (array) $query['terms'] );
+		if ( 'slug' === $query['field'] || 'name' === $query['field'] ) {
+			$query['terms'] = array_unique( (array) $query['terms'] );
+		} else {
+			$query['terms'] = wp_parse_id_list( $query['terms'] );
+		}
 
 		if ( is_taxonomy_hierarchical( $query['taxonomy'] ) && $query['include_children'] ) {
 			$this->transform_query( $query, 'term_id' );