diff --git a/src/widgets/FileDialog/mac/FileDialogPrivate.mm b/src/widgets/FileDialog/mac/FileDialogPrivate.mm
index d451f8554..ff1443505 100644
--- a/src/widgets/FileDialog/mac/FileDialogPrivate.mm
+++ b/src/widgets/FileDialog/mac/FileDialogPrivate.mm
@@ -367,6 +367,19 @@ void FileDialog::SetupExtraControls(WXWindow nativeWindow)
     {
         wxBoxSizer *verticalSizer = new wxBoxSizer( wxVERTICAL );
 
+        // FINALLY FOUND IT! Creating the panel with "this" as the parent causes
+        // an exception and stack trace to be printed to stderr:
+        //
+        //   2021-02-17 13:52:14.550 Audacity[69217:891282] warning: <NSRemoteView: 0x7f92f4e67410 com.apple.appkit.xpc.openAndSavePanelService ((null)) NSSavePanelService> ignoring attempt to mutate its subviews (
+        //      0   ViewBridge                          0x00007fff6596685d -[NSRemoteView _announceSubviewMutationDisallowed] + 29
+        //      1   libwx_osx_cocoau_debug_core-3.1.3.0 0x0000000111c3abf1 _ZN17wxWidgetCocoaImpl5EmbedEP12wxWidgetImpl + 177
+        //
+        // It's because wxPanel tries to embed the wxPanel into the NSSavePanel and
+        // that's not allowed. Everything still works fine, so it can be ignored.
+        // But, if you want to dig into it further, changing the "this" parent to
+        // GetParent() gets rid of the exception. However, events from the extra
+        // controls in the accessory view do not get handled correctly.
+
         m_filterPanel = new wxPanel( this, wxID_ANY );
         accView = m_filterPanel->GetHandle();