diff --git a/lcl/interfaces/win32/win32callback.inc b/lcl/interfaces/win32/win32callback.inc
index 2045fc0e85..d5e95f538d 100644
--- a/lcl/interfaces/win32/win32callback.inc
+++ b/lcl/interfaces/win32/win32callback.inc
@@ -1834,12 +1834,6 @@ begin
         begin
           LMessage.Result := HTTRANSPARENT;
           WinProcess := false;
-        end
-        else
-        if (lWinControl is TCustomGroupBox) then
-        begin
-          LMessage.Result := HTCLIENT;
-          WinProcess := false;
         end;
       end;
     end;
@@ -2118,7 +2112,7 @@ begin
       end;
       // cross-interface compatible: complete invalidate on resize
       if (PWindowPos(LParam)^.flags and SWP_NOSIZE) = 0 then
-        Windows.InvalidateRect(Window, nil, true);
+        Windows.InvalidateRect(Window, nil, True);
     end;
     WM_MEASUREITEM:
     begin
@@ -2163,6 +2157,11 @@ begin
         ThemeServices.IntfDoOnThemeChange;
       end;
     end;
+    WM_UPDATEUISTATE:
+    begin
+      if ThemeServices.ThemesEnabled then
+        InvalidateRect(Window, nil, True);
+    end;
 
     { >= WM_USER }
 
diff --git a/lcl/interfaces/win32/win32wscontrols.pp b/lcl/interfaces/win32/win32wscontrols.pp
index 0c0c77411a..6d25b92a76 100644
--- a/lcl/interfaces/win32/win32wscontrols.pp
+++ b/lcl/interfaces/win32/win32wscontrols.pp
@@ -627,7 +627,7 @@ end;
 class procedure TWin32WSWinControl.Invalidate(const AWinControl: TWinControl);
 begin
   // lpRect = nil updates entire client area of window
-  InvalidateRect(AWinControl.Handle, nil, true);
+  InvalidateRect(AWinControl.Handle, nil, True);
 end;
 
 class procedure TWin32WSWinControl.PaintTo(const AWinControl: TWinControl;
diff --git a/lcl/interfaces/win32/win32wsstdctrls.pp b/lcl/interfaces/win32/win32wsstdctrls.pp
index ee83b468a8..a192413d0b 100644
--- a/lcl/interfaces/win32/win32wsstdctrls.pp
+++ b/lcl/interfaces/win32/win32wsstdctrls.pp
@@ -459,20 +459,14 @@ end;
 
 function GroupBoxWindowProc(Window: HWnd; Msg: UInt; WParam: Windows.WParam;
     LParam: Windows.LParam): LResult; stdcall;
-var
-  WindowInfo: PWin32WindowInfo;
 begin
   // move groupbox specific code here
   case Msg of
-    WM_UPDATEUISTATE:
-    begin
-      if ThemeServices.ThemesEnabled then
+    WM_NCHITTEST:
       begin
-        WindowInfo := GetWin32WindowInfo(Window);
-        if (WindowInfo <> nil) and (WindowInfo^.WinControl <> nil) then
-          WindowInfo^.WinControl.Invalidate;
+        Result := HTCLIENT;
+        Exit;
       end;
-    end;
   end;
   Result := WindowProc(Window, Msg, WParam, LParam);
 end;