diff --git a/src/hooks/useSmartPolling.test.ts b/src/hooks/useSmartPolling.test.ts
new file mode 100644
index 0000000..44c4735
--- /dev/null
+++ b/src/hooks/useSmartPolling.test.ts
@@ -0,0 +1,89 @@
+import { act, renderHook } from '@testing-library/react';
+import { useSmartPolling } from './useSmartPolling';
+
+describe('useSmartPolling (#570)', () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+  });
+
+  afterEach(() => {
+    jest.useRealTimers();
+  });
+
+  it('starts polling when enabled=true', async () => {
+    const fetchFn = jest.fn().mockResolvedValue('data-1');
+    const { result, unmount } = renderHook(() =>
+      useSmartPolling({ fetchFn, interval: 1000, enabled: true })
+    );
+
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    expect(result.current.isPolling).toBe(true);
+    expect(fetchFn).toHaveBeenCalled();
+
+    unmount();
+  });
+
+  it('sets isPolling=false and stops timer when toggled to enabled=false (#570)', async () => {
+    const fetchFn = jest.fn().mockResolvedValue('data-1');
+    const { result, rerender, unmount } = renderHook(
+      ({ enabled }) => useSmartPolling({ fetchFn, interval: 1000, enabled }),
+      { initialProps: { enabled: true } }
+    );
+
+    await act(async () => {
+      await Promise.resolve();
+    });
+    expect(result.current.isPolling).toBe(true);
+
+    // Toggle enabled to false
+    act(() => {
+      rerender({ enabled: false });
+    });
+
+    expect(result.current.isPolling).toBe(false);
+
+    const callCountBefore = fetchFn.mock.calls.length;
+    act(() => {
+      jest.advanceTimersByTime(5000);
+    });
+    expect(fetchFn.mock.calls.length).toBe(callCountBefore);
+
+    unmount();
+  });
+
+  it('re-starts polling immediately when toggled from false back to true (#570)', async () => {
+    const fetchFn = jest.fn().mockResolvedValue('data-1');
+    const { result, rerender, unmount } = renderHook(
+      ({ enabled }) => useSmartPolling({ fetchFn, interval: 1000, enabled }),
+      { initialProps: { enabled: true } }
+    );
+
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    // Disable
+    act(() => {
+      rerender({ enabled: false });
+    });
+    expect(result.current.isPolling).toBe(false);
+
+    // Re-enable
+    const callsBeforeReenable = fetchFn.mock.calls.length;
+    act(() => {
+      rerender({ enabled: true });
+    });
+
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    expect(result.current.isPolling).toBe(true);
+    expect(fetchFn.mock.calls.length).toBeGreaterThan(callsBeforeReenable);
+
+    unmount();
+  });
+});
diff --git a/src/hooks/useSmartPolling.ts b/src/hooks/useSmartPolling.ts
index 81507fc..779c670 100644
--- a/src/hooks/useSmartPolling.ts
+++ b/src/hooks/useSmartPolling.ts
@@ -39,12 +39,16 @@ const pollingInitialState: PollingState = {
 function pollingReducer(state: PollingState, action: PollingAction): PollingState {
   switch (action.type) {
     case 'START_POLLING':
+      if (state.isPolling) return state;
       return { ...state, isPolling: true };
     case 'STOP_POLLING':
+      if (!state.isPolling) return state;
       return { ...state, isPolling: false };
     case 'START_BACKOFF':
+      if (state.isBackingOff) return state;
       return { ...state, isBackingOff: true };
     case 'STOP_BACKOFF':
+      if (!state.isBackingOff) return state;
       return { ...state, isBackingOff: false };
     default:
       return state;
@@ -73,17 +77,26 @@ export function useSmartPolling<T>({
   const previousDataRef = useRef<T | null>(null);
   const isBackgroundedRef = useRef(false);
 
+  const fetchFnRef = useRef(fetchFn);
+  fetchFnRef.current = fetchFn;
+
+  const compareFnRef = useRef(compareFn);
+  compareFnRef.current = compareFn;
+
+  const onDataChangeRef = useRef(onDataChange);
+  onDataChangeRef.current = onDataChange;
+
   const fetchData = useCallback(async () => {
     if (!isMountedRef.current) return;
     
     try {
       setIsLoading(true);
-      const result = await fetchFn();
+      const result = await fetchFnRef.current();
       
       if (!isMountedRef.current) return;
 
       const hasChanged = previousDataRef.current !== null 
-        ? !compareFn(previousDataRef.current, result)
+        ? !compareFnRef.current(previousDataRef.current, result)
         : true;
 
       if (hasChanged) {
@@ -92,7 +105,7 @@ export function useSmartPolling<T>({
         unchangedCountRef.current = 0;
         currentIntervalRef.current = interval;
         dispatch({ type: 'STOP_BACKOFF' });
-        onDataChange?.(result);
+        onDataChangeRef.current?.(result);
       } else {
         unchangedCountRef.current += 1;
         
@@ -118,7 +131,7 @@ export function useSmartPolling<T>({
         setIsLoading(false);
       }
     }
-  }, [fetchFn, compareFn, interval, backoffMultiplier, maxBackoff, unchangedThreshold, onDataChange]);
+  }, [interval, backoffMultiplier, maxBackoff, unchangedThreshold]);
 
   const refetch = useCallback(async () => {
     currentIntervalRef.current = interval;
@@ -127,6 +140,18 @@ export function useSmartPolling<T>({
     await fetchData();
   }, [fetchData, interval]);
 
+  // Unmount-only cleanup guard (#361)
+  useEffect(() => {
+    isMountedRef.current = true;
+    return () => {
+      isMountedRef.current = false;
+      if (intervalRef.current) {
+        clearInterval(intervalRef.current);
+        intervalRef.current = null;
+      }
+    };
+  }, []);
+
   // Handle visibility change
   useEffect(() => {
     const handleVisibilityChange = () => {
@@ -154,31 +179,36 @@ export function useSmartPolling<T>({
     };
   }, [enabled, fetchData]);
 
-  // Main polling effect - use a ref to track initial mount
-  const hasInitialized = useRef(false);
-
+  // Main polling effect for enabled state (#570)
   useEffect(() => {
-    isMountedRef.current = true;
-
     if (!enabled) {
+      if (intervalRef.current) {
+        clearInterval(intervalRef.current);
+        intervalRef.current = null;
+      }
+      if (isMountedRef.current) {
+        dispatch({ type: 'STOP_POLLING' });
+      }
       return;
     }
 
-    // Only start polling on initial mount or when enabled changes
-    if (!hasInitialized.current) {
-      hasInitialized.current = true;
-      dispatch({ type: 'START_POLLING' });
-      fetchData();
-      intervalRef.current = setInterval(fetchData, currentIntervalRef.current);
+    if (isBackgroundedRef.current) {
+      return;
     }
 
+    dispatch({ type: 'START_POLLING' });
+    fetchData();
+
+    if (intervalRef.current) {
+      clearInterval(intervalRef.current);
+    }
+    intervalRef.current = setInterval(fetchData, currentIntervalRef.current);
+
     return () => {
-      isMountedRef.current = false;
       if (intervalRef.current) {
         clearInterval(intervalRef.current);
         intervalRef.current = null;
       }
-      // Don't dispatch STOP_POLLING here to avoid state updates during unmount
     };
   }, [enabled, fetchData]);