diff --git a/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift b/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift
index db667128..64e241f6 100644
--- a/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift
+++ b/Packages/vChewing_CandidateWindow/Sources/CandidateWindow/TDKCandidates/CtlCandidateTDK.swift
@@ -24,6 +24,7 @@ private extension NSUserInterfaceLayoutOrientation {
 }
 
 public class CtlCandidateTDK: CtlCandidate, NSWindowDelegate {
+  @objc var observation: NSKeyValueObservation?
   public var maxLinesPerPage: Int = 0
   public var useCocoa: Bool = false
   public var useMouseScrolling: Bool = true
@@ -72,6 +73,10 @@ public class CtlCandidateTDK: CtlCandidate, NSWindowDelegate {
     Self.currentWindow = panel
     window?.delegate = self
     currentLayout = layout
+
+    observation = Broadcaster.shared.observe(\.eventForClosingAllPanels, options: [.new]) { _, _ in
+      self.visible = false
+    }
   }
 
   @available(*, unavailable)
diff --git a/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift b/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift
index 748b2643..72b87070 100644
--- a/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift
+++ b/Packages/vChewing_MainAssembly/Sources/MainAssembly/SessionCtl_Core.swift
@@ -26,6 +26,8 @@ import TooltipUI
 /// 輸入會話創建一個控制器型別。因此，對於每個輸入會話，都有一個對應的 IMKInputController。
 @objc(SessionCtl) // 必須加上 ObjC，因為 IMK 是用 ObjC 寫的。
 public class SessionCtl: IMKInputController {
+  public weak static var current: SessionCtl?
+
   /// 標記狀態來聲明目前新增的詞彙是否需要賦以非常低的權重。
   public static var areWeNerfing = false
 
@@ -219,6 +221,9 @@ public class SessionCtl: IMKInputController {
   private func construct(client theClient: (IMKTextInput & NSObjectProtocol)? = nil) {
     DispatchQueue.main.async { [weak self] in
       guard let self = self else { return }
+      // 關掉所有之前的副本的視窗。
+      Self.current?.hidePalettes()
+      Self.current = self
       self.inputHandler = InputHandler(
         lm: LMMgr.currentLM, uom: LMMgr.currentUOM, pref: PrefMgr.shared
       )
@@ -479,8 +484,12 @@ public extension SessionCtl {
 
   /// 該函式僅用來取消任何輸入法浮動視窗的顯示。
   override func hidePalettes() {
-    candidateUI?.visible = false
-    popupCompositionBuffer.hide()
-    tooltipInstance.hide()
+    Broadcaster.shared.eventForClosingAllPanels = .init()
+    // 因為上述變數受選字窗、浮動組字窗、工具提示視窗所實時觀測，
+    // 所以他們會在看到該變數有變化時自行關閉。
+    // 自然不需要下述三行。
+    // candidateUI?.visible = false
+    // popupCompositionBuffer.hide()
+    // tooltipInstance.hide()
   }
 }
diff --git a/Packages/vChewing_Shared/Sources/Shared/Broadcaster.swift b/Packages/vChewing_Shared/Sources/Shared/Broadcaster.swift
index a942fe71..e9ae798f 100644
--- a/Packages/vChewing_Shared/Sources/Shared/Broadcaster.swift
+++ b/Packages/vChewing_Shared/Sources/Shared/Broadcaster.swift
@@ -13,4 +13,5 @@ import AppKit
 @objcMembers public class Broadcaster: NSObject {
   public static var shared = Broadcaster()
   public dynamic var eventForReloadingPhraseEditor = UUID()
+  public dynamic var eventForClosingAllPanels = UUID()
 }
diff --git a/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_EarlyCocoa.swift b/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_EarlyCocoa.swift
index 6e94c6a7..84b3b166 100644
--- a/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_EarlyCocoa.swift
+++ b/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_EarlyCocoa.swift
@@ -10,6 +10,7 @@ import AppKit
 import Shared
 
 public class TooltipUI_EarlyCocoa: NSWindowController, TooltipUIProtocol {
+  @objc var observation: NSKeyValueObservation?
   private var messageText: NSTextField
   private var tooltip: String = "" {
     didSet {
@@ -100,6 +101,10 @@ public class TooltipUI_EarlyCocoa: NSWindowController, TooltipUIProtocol {
     panel.contentView?.addSubview(messageText)
     Self.currentWindow = panel
     super.init(window: panel)
+
+    observation = Broadcaster.shared.observe(\.eventForClosingAllPanels, options: [.new]) { _, _ in
+      self.hide()
+    }
   }
 
   @available(*, unavailable)
diff --git a/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_LateCocoa.swift b/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_LateCocoa.swift
index 4aef3645..f966da81 100644
--- a/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_LateCocoa.swift
+++ b/Packages/vChewing_TooltipUI/Sources/TooltipUI/TooltipUI_LateCocoa.swift
@@ -12,6 +12,7 @@ import NSAttributedTextView
 import Shared
 
 public class TooltipUI_LateCocoa: NSWindowController, TooltipUIProtocol {
+  @objc var observation: NSKeyValueObservation?
   private var messageText: NSAttributedTooltipTextView
   private var tooltip: String = "" {
     didSet {
@@ -55,6 +56,10 @@ public class TooltipUI_LateCocoa: NSWindowController, TooltipUIProtocol {
     panel.contentView?.addSubview(messageText)
     Self.currentWindow = panel
     super.init(window: panel)
+
+    observation = Broadcaster.shared.observe(\.eventForClosingAllPanels, options: [.new]) { _, _ in
+      self.hide()
+    }
   }
 
   @available(*, unavailable)