diff --git a/js/calendar.js b/js/calendar.js
index f1340b1..cc12243 100644
--- a/js/calendar.js
+++ b/js/calendar.js
@@ -1,6 +1,6 @@
 import { state } from './app.js';
 import { getWorkdays, generatePlan } from './algorithm.js';
-import { toggleHoliday, toggleClosure, addHistoryEntries } from './data.js';
+import { toggleHoliday, toggleClosure, addHistoryEntries, removeHistoryEntry } from './data.js';
 import { exportSchedule, downloadBlob } from './excel.js';
 
 const MONTHS = ['Januar','Februar','März','April','Mai','Juni',
@@ -106,7 +106,7 @@ function loadPlanFromHistory() {
   const prefix = currentYear + '-' + String(currentMonth).padStart(2,'0');
   currentPlan = state.history
     .filter(h => h.date.startsWith(prefix))
-    .map(h => ({ ...h }));
+    .slice();
 }
 
 function renderGrid(wrapper, exportBtn) {
@@ -208,7 +208,7 @@ function renderGrid(wrapper, exportBtn) {
             const idx = currentPlan.findIndex(a => a.date === iso);
             if (idx >= 0) currentPlan[idx] = entry; else currentPlan.push(entry);
           } else {
-            state.history = state.history.filter(h => h.date !== iso);
+            removeHistoryEntry(state, iso);
             currentPlan = currentPlan.filter(a => a.date !== iso);
           }
           exportBtn.style.display = currentPlan.length > 0 ? 'inline-block' : 'none';