Fix the bug

Author: zadjii-msft

src/cascadia/TerminalControl/ControlInteractivity.cpp

@@ -255,10 +255,21 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         }
         else if (WI_IsFlagSet(buttonState, MouseButtonState::IsRightButtonDown))
         {
-            // Try to copy the text and clear the selection
-            const auto successfulCopy = CopySelectionToClipboard(shiftEnabled, nullptr);
+            const auto copyOnSelect{ _core->CopyOnSelect() };
+            bool successfulCopy = false;
+
+            // Don't try to copy if we're in copyOnSelect mode and have already
+            // copied this selection. GH#14464 demonstrates a scenario where the
+            // buffer contents might have changed since the selection was made,
+            // and copying here would cause weirdness.
+            if (_selectionNeedsToBeCopied || !copyOnSelect)
+            {
+                // Try to copy the text and clear the selection
+                successfulCopy = CopySelectionToClipboard(shiftEnabled, nullptr);
+            }
             _core->ClearSelection();
-            if (_core->CopyOnSelect() || !successfulCopy)
+
+            if (copyOnSelect || !successfulCopy)
             {
                 // CopyOnSelect: right click always pastes!
                 // Otherwise: no selection --> paste

src/cascadia/UnitTests_Control/ControlInteractivityTests.cpp

@@ -1041,6 +1041,9 @@ namespace ControlUnitTests
         VERIFY_IS_TRUE(core->HasSelection());
 
         Log::Comment(L" --- Right-click to paste --- ");
+        // Note from GH#14464: we don't want to copy _again_ at this point. The
+        // copy occured when the selection was made, we shouldn't stealth-update
+        // the clipboard again.
         expectedCopyContents = std::nullopt;
         expectedPaste = true;
         interactivity->PointerPressed(rightMouseDown,
@@ -1053,6 +1056,9 @@ namespace ControlUnitTests
 
     void ControlInteractivityTests::CopyOnSelectAltBuffer()
     {
+        // This test was inspired by GH#14464. Ultimately, it's similar to the
+        // CopyOnSelectSimple, just with an alt buffer, and outputting text
+        // after the selection was made.
         auto [settings, conn] = _createSettingsAndConnection();
         settings->CopyOnSelect(true);
         auto [core, interactivity] = _createCoreAndInteractivity(*settings, *conn);