diff --git a/RavelCAPI b/RavelCAPI
index edbdf36c6..84764879e 160000
--- a/RavelCAPI
+++ b/RavelCAPI
@@ -1 +1 @@
-Subproject commit edbdf36c6ce7f1a2cd597b06f8da0c529961cddb
+Subproject commit 84764879eb36f7e52cef362561fe64d0f9077d95
diff --git a/model/windowInformation.cc b/model/windowInformation.cc
index 7b13419b9..3c7c28366 100644
--- a/model/windowInformation.cc
+++ b/model/windowInformation.cc
@@ -82,7 +82,11 @@ namespace minsky
       HDC dc=BeginPaint(winfo.childWindowId, &ps);
       BitBlt(dc, x, y, width,height,winfo.hdcMem,x,y,SRCCOPY);
       EndPaint(winfo.childWindowId, &ps);
-      SetWindowPos(winfo.childWindowId,HWND_TOP,winfo.offsetLeft,winfo.offsetTop,winfo.childWidth,winfo.childHeight,0);
+      // Note: SetWindowPos was previously called here on every blit to keep the
+      // child window at HWND_TOP, but that fired WM_WINDOWPOSCHANGED on every
+      // paint which could cascade into further WM_PAINT messages and interact
+      // badly with screen-sharing hooks (e.g. Zoom).  The window is already
+      // positioned correctly at creation time in WindowInformation().
 #elif defined(USE_X11)
       static mutex blitting;
       const lock_guard<mutex> lock(blitting);
@@ -159,6 +163,12 @@ namespace minsky
           if (GetUpdateRect(hwnd,&r,false))
             blit(*winfo, r.left, r.top, r.right-r.left, r.bottom-r.top);
         }
+        else
+          // GWLP_USERDATA is zeroed in ~WindowInformation before the window is
+          // closed, so reaching here means the WindowInformation has already been
+          // torn down.  Validate the rect so Windows stops generating WM_PAINT
+          // messages for a window that no longer has a backing buffer.
+          ValidateRect(hwnd, nullptr);
         return 0;
       case WM_NCHITTEST:
         return HTTRANSPARENT;
diff --git a/schema/optional.h b/schema/optional.h
index 6ad916586..5206f98da 100644
--- a/schema/optional.h
+++ b/schema/optional.h
@@ -77,7 +77,7 @@ namespace classdesc
   void xsd_generate(xsd_generate_t& g, const string& d, const minsky::Optional<T>& a) 
   {
     xsd_generate_t::Optional o(g,true);
-    T tmp; // a may be null
+    T tmp{}; // a may be null
     xsd_generate(g,d,tmp);
   }
 
diff --git a/test/testMinsky.cc b/test/testMinsky.cc
index 15cef020f..affccabf4 100644
--- a/test/testMinsky.cc
+++ b/test/testMinsky.cc
@@ -1270,7 +1270,7 @@ TEST(TensorOps, evalOpEvaluate)
 
       // renaming just the canvas variable should change  it's type
       canvas.item=stockVar;
-      if (auto v=canvas.item->variableCast())
+      if (canvas.item->variableCast())
         {
           canvas.renameItem("foo");
           EXPECT_TRUE(canvas.item && canvas.item->variableCast());
diff --git a/test/testPubTab.cc b/test/testPubTab.cc
index a49a7e62b..7711ca274 100644
--- a/test/testPubTab.cc
+++ b/test/testPubTab.cc
@@ -157,7 +157,7 @@ TEST_F(PubTabSuite,removeSelf)
          load("1Free.mky");
          // send the Godley table to the pub tab
          for (auto& i: model->items)
-           if (auto g=dynamic_cast<GodleyIcon*>(i.get()))
+           if (dynamic_cast<GodleyIcon*>(i.get()))
              {
                publicationTabs[0].items.emplace_back(i);
                break;