diff --git a/app.py b/app.py
index 566ab93..40b600f 100644
--- a/app.py
+++ b/app.py
@@ -76,6 +76,7 @@ copy_state = {
     'phase': 'idle',
 }
 copy_lock = threading.Lock()
+_copy_thread: threading.Thread | None = None
 
 def load_state():
     global copy_state
@@ -922,16 +923,20 @@ def r_status():
 
 @app.route('/api/copy/start', methods=['POST'])
 def r_start():
+    global _copy_thread
     with copy_lock:
         if copy_state['running']:
             return jsonify(error='Bereits aktiv'), 400
+    if _copy_thread is not None and _copy_thread.is_alive():
+        return jsonify(error='Abbruch läuft noch, bitte einen Moment warten'), 400
     cfg  = load_cfg()
     devs = usb_devices()
     src  = next((d for d in devs if d['usb_port'] == cfg.get('source_port')), None)
     dst  = next((d for d in devs if d['usb_port'] == cfg.get('dest_port')), None)
     if not src: return jsonify(error='Quellgerät nicht gefunden'), 400
     if not dst: return jsonify(error='Zielgerät nicht gefunden'), 400
-    threading.Thread(target=do_copy, args=(src, dst, cfg), daemon=True).start()
+    _copy_thread = threading.Thread(target=do_copy, args=(src, dst, cfg), daemon=True)
+    _copy_thread.start()
     return jsonify(ok=True)
 
 @app.route('/api/copy/cancel', methods=['POST'])
@@ -2306,7 +2311,7 @@ async function poll(){
       }
       sum.textContent=''; bS.style.display='none'; bC.style.display=''; time.textContent='';
     }else{
-      bS.style.display=''; bC.style.display=''; cf.textContent='';
+      bS.style.display=''; bC.style.display='none'; cf.textContent='';
       eta.style.display='none'; spd.style.display='none'; pfiles.style.display='none'; pbytes.style.display='none'; pp.style.display='none';
       if(c.error){
         tx.className='st-headline st-err'; tx.textContent='Fehler: '+c.error;