diff --git a/tests/integration/PostEntityLifecycleTest.php b/tests/integration/PostEntityLifecycleTest.php
index 345e89c..097c951 100644
--- a/tests/integration/PostEntityLifecycleTest.php
+++ b/tests/integration/PostEntityLifecycleTest.php
@@ -150,6 +150,10 @@ class PostEntityLifecycleTest extends TestCase {
 		$wpdb->query( 'TRUNCATE TABLE `' . self::POSTS . '`' );
 		$wpdb->query( 'TRUNCATE TABLE `' . self::POSTMETA . '`' );
 		$wpdb->query( 'TRUNCATE TABLE `' . self::FLAT . '`' );
+
+		// Other classes create/drop sibling flat tables (e.g. wpdo_post_attachment):
+		// a stale table_exists() cache would make diagnose() COUNT a dropped table.
+		TMDO_Schema_Manager::flush_table_exists_cache();
 	}
 
 	private static function class_for( string $rel ): ?string {
diff --git a/tests/integration/PostMigrationTest.php b/tests/integration/PostMigrationTest.php
index f10edef..164a118 100644
--- a/tests/integration/PostMigrationTest.php
+++ b/tests/integration/PostMigrationTest.php
@@ -114,6 +114,10 @@ class PostMigrationTest extends TestCase {
 		$wpdb->query( 'TRUNCATE TABLE `' . self::POSTS . '`' );
 		$wpdb->query( 'TRUNCATE TABLE `' . self::POSTMETA . '`' );
 		$wpdb->query( 'TRUNCATE TABLE `' . self::FLAT . '`' );
+
+		// Other classes create/drop sibling flat tables (e.g. wpdo_post_attachment):
+		// a stale table_exists() cache would make diagnose() COUNT a dropped table.
+		TMDO_Schema_Manager::flush_table_exists_cache();
 	}
 
 	private function seed_post( int $id, string $post_type ): void {