diff --git a/fpdfsdk/pwl/cpwl_combo_box.cpp b/fpdfsdk/pwl/cpwl_combo_box.cpp
index 0d42120..c84b7c0 100644
--- a/fpdfsdk/pwl/cpwl_combo_box.cpp
+++ b/fpdfsdk/pwl/cpwl_combo_box.cpp
@@ -344,31 +344,42 @@
   if (!m_pEdit)
     return false;
 
+  ObservedPtr<CPWL_Wnd> thisObserved(this);
   m_nSelectItem = -1;
 
   switch (nKeyCode) {
     case FWL_VKEY_Up:
       if (m_pList->GetCurSel() > 0) {
-        if (GetFillerNotify()->OnPopupPreOpen(GetAttachedData(), nFlag))
+        if (GetFillerNotify()->OnPopupPreOpen(GetAttachedData(), nFlag) ||
+            !thisObserved) {
           return false;
-        if (GetFillerNotify()->OnPopupPostOpen(GetAttachedData(), nFlag))
+        }
+        if (GetFillerNotify()->OnPopupPostOpen(GetAttachedData(), nFlag) ||
+            !thisObserved) {
           return false;
+        }
         if (m_pList->IsMovementKey(nKeyCode)) {
-          if (m_pList->OnMovementKeyDown(nKeyCode, nFlag))
+          if (m_pList->OnMovementKeyDown(nKeyCode, nFlag) || !thisObserved) {
             return false;
+          }
           SetSelectText();
         }
       }
       return true;
     case FWL_VKEY_Down:
       if (m_pList->GetCurSel() < m_pList->GetCount() - 1) {
-        if (GetFillerNotify()->OnPopupPreOpen(GetAttachedData(), nFlag))
+        if (GetFillerNotify()->OnPopupPreOpen(GetAttachedData(), nFlag) ||
+            !thisObserved) {
           return false;
-        if (GetFillerNotify()->OnPopupPostOpen(GetAttachedData(), nFlag))
+        }
+        if (GetFillerNotify()->OnPopupPostOpen(GetAttachedData(), nFlag) ||
+            !thisObserved) {
           return false;
+        }
         if (m_pList->IsMovementKey(nKeyCode)) {
-          if (m_pList->OnMovementKeyDown(nKeyCode, nFlag))
+          if (m_pList->OnMovementKeyDown(nKeyCode, nFlag) || !thisObserved) {
             return false;
+          }
           SetSelectText();
         }
       }
@@ -420,10 +431,15 @@
   if (HasFlag(PCBS_ALLOWCUSTOMTEXT))
     return m_pEdit->OnChar(nChar, nFlag);
 
-  if (GetFillerNotify()->OnPopupPreOpen(GetAttachedData(), nFlag))
+  ObservedPtr<CPWL_Wnd> thisObserved(this);
+  if (GetFillerNotify()->OnPopupPreOpen(GetAttachedData(), nFlag) ||
+      !thisObserved) {
     return false;
-  if (GetFillerNotify()->OnPopupPostOpen(GetAttachedData(), nFlag))
+  }
+  if (GetFillerNotify()->OnPopupPostOpen(GetAttachedData(), nFlag) ||
+      !thisObserved) {
     return false;
+  }
   if (!m_pList->IsChar(nChar, nFlag))
     return false;
   return m_pList->OnCharNotify(nChar, nFlag);
diff --git a/testing/resources/javascript/bug_1445426.evt b/testing/resources/javascript/bug_1445426.evt
new file mode 100644
index 0000000..265e85b
--- /dev/null
+++ b/testing/resources/javascript/bug_1445426.evt
@@ -0,0 +1,3 @@
+mousedown,left,202,697
+mouseup,left,202,697
+keycode,40
diff --git a/testing/resources/javascript/bug_1445426.in b/testing/resources/javascript/bug_1445426.in
new file mode 100644
index 0000000..1483da7
--- /dev/null
+++ b/testing/resources/javascript/bug_1445426.in
@@ -0,0 +1,114 @@
+{{header}}
+{{object 1 0}} <<
+  /Type /Catalog
+  /Pages 2 0 R
+  /AcroForm 4 0 R
+  /OpenAction 40 0 R
+>>
+endobj
+{{object 2 0}} <<
+  /Type /Pages
+  /Count 2
+  /Kids [
+    32 0 R
+    34 0 R
+  ]
+>>
+endobj
+% Forms
+{{object 4 0}} <<
+  /Fields [
+    10 0 R
+    11 0 R
+  ]
+>>
+endobj
+% Fields
+{{object 10 0}} <<
+  /Type /Annot
+  /Subtype /Widget
+  /FT /Tx
+  /T (Field_TextEdit)
+  /Rect [0 0 612 792]
+>>
+{{object 11 0}} <<
+  /T (Field_ComboBox)
+  /Parent 4 0 R
+  /Kids [12 0 R]
+  /Opt [(a) (b) (c) (d)]
+  /V [(a)]
+>>
+endobj
+{{object 12 0}} <<
+  /Type /Annot
+  /Subtype /Widget
+  /FT /Ch
+  /Ff 131072
+  /Parent 11 0 R
+  /Kids [13 0 R]
+>>
+endobj
+{{object 13 0}} <<
+  /Parent 12 0 R
+  /Type /Annot
+  /Subtype /Widget
+  /Rect [0 0 612 792]
+  /AA << /K 20 0 R >>
+>>
+endobj
+% Pages
+{{object 32 0}} <<
+  /Type /Page
+  /Parent 2 0 R
+  /MediaBox [0 0 612 792]
+  /Annots [13 0 R]
+
+>>
+endobj
+{{object 34 0}} <<
+  /Type /Page
+  /Parent 2 0 R
+  /MediaBox [0 0 612 792]
+  /Annots [10 0 R]
+>>
+endobj
+% Document JS Action
+{{object 40 0}} <<
+  /Type /Action
+  /S /JavaScript
+  /JS 41 0 R
+>>
+endobj
+% JS program to exexute
+{{object 41 0}} <<
+  {{streamlen}}
+>>
+stream
+var field_text = this.getField("Field_TextEdit");
+var field_combobox = this.getField("Field_ComboBox");
+field_combobox.setFocus();
+this.__defineGetter__("filesize", function new_getter(){
+                                    field_text.setFocus();
+                                    field_combobox.borderStyle="dashed";
+                                    field_combobox.setFocus();
+                                  });
+endstream
+endobj
+% OpenAction action
+{{object 20 0}} <<
+  /S /JavaScript
+  /JS 21 0 R
+>>
+endobj
+% JS program to exexute
+{{object 21 0}} <<
+  {{streamlen}}
+>>
+stream
+var t = this.filesize;
+endstream
+endobj
+{{xref}}
+{{trailer}}
+{{startxref}}
+%%EOF