diff --git a/src/modules/admin/pages/courses/lessons/LessonPageBuilder.jsx b/src/modules/admin/pages/courses/lessons/LessonPageBuilder.jsx
index 0f861fc..0a27574 100644
--- a/src/modules/admin/pages/courses/lessons/LessonPageBuilder.jsx
+++ b/src/modules/admin/pages/courses/lessons/LessonPageBuilder.jsx
@@ -37,7 +37,13 @@ export default function LessonPageBuilder() {
   const blocksSeeded = useRef(false);
 
   useEffect(() => {
+    // The builder stays mounted across lesson navigations (route param change
+    // only), so local editor state must be reset by hand here — otherwise the
+    // previous lesson's blocks leak into the next lesson's editor.
     (async () => {
+      setInitializing(true);
+      setBlocks([]);
+      blocksSeeded.current = false;
       await fetchLesson(courseId, unitId, lessonId);
       setInitializing(false);
     })();