diff --git a/j3270/src/main/java/haus/nightmare/j3270/J3270App.java b/j3270/src/main/java/haus/nightmare/j3270/J3270App.java
index d500c89..30bf7af 100644
--- a/j3270/src/main/java/haus/nightmare/j3270/J3270App.java
+++ b/j3270/src/main/java/haus/nightmare/j3270/J3270App.java
@@ -945,8 +945,14 @@ public class J3270App extends JFrame implements ConnectionListener, ScreenUpdate
     }
 
     public boolean isConnected() {
-        return client != null && (client.isConnected() ||
-                (client.getConnectionState() != null && client.getConnectionState().isConnected()));
+        if (client == null) {
+            return false;
+        }
+        ConnectionState state = client.getConnectionState();
+        if (state == null || state == ConnectionState.NOT_CONNECTED) {
+            return false;
+        }
+        return client.isConnected() || state.isConnected();
     }
 
     public String getConnectedTarget() {
@@ -1213,6 +1219,7 @@ public class J3270App extends JFrame implements ConnectionListener, ScreenUpdate
                 setTitle("j3270 — " + lastHost + ":" + lastPort + " [Reconnecting...]");
             } else if (newState == ConnectionState.NOT_CONNECTED) {
                 setTitle("j3270 — Java TN3270 Terminal Emulator");
+                syncModeMenuItems();
             } else if (newState.isFullSession() && !oldState.isFullSession()) {
                 String tlsIndicator = (client != null && client.getConfig().isUseTls()) ?
                         (client.getConfig().isTlsVerifyCert() ? " [TLS]" : " [TLS/Unverified]") : "";
diff --git a/j3270/src/test/java/haus/nightmare/j3270/ConnectionConflictTest.java b/j3270/src/test/java/haus/nightmare/j3270/ConnectionConflictTest.java
index f773f06..485a871 100644
--- a/j3270/src/test/java/haus/nightmare/j3270/ConnectionConflictTest.java
+++ b/j3270/src/test/java/haus/nightmare/j3270/ConnectionConflictTest.java
@@ -294,4 +294,35 @@ public class ConnectionConflictTest {
         assertEquals(haus.nightmare.lib3270j.ConnectionState.NOT_CONNECTED, client.getConnectionState());
         assertFalse(client.isConnected());
     }
+
+    @Test
+    @DisplayName("When not connected, connect does not trigger abort connection dialog for previously closed connection")
+    public void testNotConnectedDoesNotTriggerAbortDialog() throws Exception {
+        J3270App app = createApp();
+        if (app == null) return;
+
+        // Simulate a previously closed connection
+        ConnectionConfig config1 = new ConnectionConfig("host1.test", 23, TerminalModel.IBM_3278_2);
+        app.connect(config1, false);
+
+        Telnet3270Client client = app.getClient();
+        assertNotNull(client);
+        // Force the client's FSM state to NOT_CONNECTED, simulating connection closure
+        client.getTelnetFSM().setConnectionState(haus.nightmare.lib3270j.ConnectionState.NOT_CONNECTED);
+
+        assertFalse(app.isConnected(), "app.isConnected() must return false when client is NOT_CONNECTED");
+
+        boolean[] handlerCalled = new boolean[]{false};
+        app.setConnectChoiceHandler((owner, target) -> {
+            handlerCalled[0] = true;
+            return ConnectChoiceDialog.Choice.CANCEL;
+        });
+
+        // Initiate a new connection
+        ConnectionConfig config2 = new ConnectionConfig("host2.test", 23, TerminalModel.IBM_3278_2);
+        app.connect(config2, true);
+
+        assertFalse(handlerCalled[0], "Connect choice handler must NOT be called when j3270 is not connected");
+        assertEquals("host2.test", app.getClient().getConfig().getHost(), "Must proceed to connect to host2.test in same window");
+    }
 }
diff --git a/lib3270j/src/main/java/haus/nightmare/lib3270j/Telnet3270Client.java b/lib3270j/src/main/java/haus/nightmare/lib3270j/Telnet3270Client.java
index 2e9a124..b9afbad 100644
--- a/lib3270j/src/main/java/haus/nightmare/lib3270j/Telnet3270Client.java
+++ b/lib3270j/src/main/java/haus/nightmare/lib3270j/Telnet3270Client.java
@@ -385,6 +385,9 @@ public class Telnet3270Client {
      * Check if connected (any state past TCP pending).
      */
     public boolean isConnected() {
+        if (fsm != null && fsm.getConnectionState() == ConnectionState.NOT_CONNECTED) {
+            return false;
+        }
         return connection != null && connection.isConnected();
     }
 
diff --git a/lib3270j/src/main/java/haus/nightmare/lib3270j/telnet/TelnetConnection.java b/lib3270j/src/main/java/haus/nightmare/lib3270j/telnet/TelnetConnection.java
index 971493e..021a348 100644
--- a/lib3270j/src/main/java/haus/nightmare/lib3270j/telnet/TelnetConnection.java
+++ b/lib3270j/src/main/java/haus/nightmare/lib3270j/telnet/TelnetConnection.java
@@ -599,7 +599,7 @@ public class TelnetConnection {
      * Check if the socket is connected.
      */
     public boolean isConnected() {
-        return socket != null && socket.isConnected() && !socket.isClosed();
+        return running && socket != null && socket.isConnected() && !socket.isClosed();
     }
 
     /**
@@ -654,7 +654,13 @@ public class TelnetConnection {
                 fsm.onError("Network loop error: " + t.getMessage());
             }
         } finally {
+            running = false;
             stopKeepAlive();
+            try {
+                if (socket != null && !socket.isClosed()) {
+                    socket.close();
+                }
+            } catch (IOException ignored) {}
         }
     }
 
diff --git a/lib3270j/src/test/java/haus/nightmare/lib3270j/testutil/Mock3270ServerIntegrationTest.java b/lib3270j/src/test/java/haus/nightmare/lib3270j/testutil/Mock3270ServerIntegrationTest.java
index b1ce9b5..eaff8e4 100644
--- a/lib3270j/src/test/java/haus/nightmare/lib3270j/testutil/Mock3270ServerIntegrationTest.java
+++ b/lib3270j/src/test/java/haus/nightmare/lib3270j/testutil/Mock3270ServerIntegrationTest.java
@@ -335,4 +335,24 @@ public class Mock3270ServerIntegrationTest {
         }
         assertTrue(receivedWontOrDontTn3270e, "Server should have received Telnet de-negotiation for TN3270E");
     }
+
+    @Test
+    public void testServerSideDisconnectTransitionsClientToNotConnectedAndClosesSocket() throws Exception {
+        ConnectionConfig config = new ConnectionConfig("127.0.0.1", server.getPort(), TerminalModel.IBM_3279_2);
+        client = new Telnet3270Client(config);
+        assertTrue(client.connect(8000));
+        assertTrue(server.waitForHandshake(5, TimeUnit.SECONDS));
+        waitForState(client, ConnectionState.CONNECTED_TN3270E, 5000);
+        assertTrue(client.isConnected());
+
+        // Server drops connection (host disconnect)
+        server.disconnectClient();
+
+        // Wait for client to detect disconnect
+        waitForState(client, ConnectionState.NOT_CONNECTED, 5000);
+        assertEquals(ConnectionState.NOT_CONNECTED, client.getConnectionState());
+        assertFalse(client.isConnected(), "Client must report isConnected() == false after host disconnect");
+        assertNotNull(client.getConnection());
+        assertFalse(client.getConnection().isConnected(), "TelnetConnection must report isConnected() == false after host disconnect");
+    }
 }