https://github.com/fcitx/fcitx-qt5/commit/6f2033c497fe0da1fd197bc3be35695b11eafd93

--- a/platforminputcontext/qfcitxplatforminputcontext.cpp
+++ b/platforminputcontext/qfcitxplatforminputcontext.cpp
@@ -291,8 +291,21 @@
         return;
     }
     if (proxy) {
-        cursorRectChanged();
         proxy->focusIn();
+        // We need to delegate this otherwise it may cause self-recursion in
+        // certain application like libreoffice.
+        auto window = m_lastWindow;
+        QMetaObject::invokeMethod(
+            this,
+            [this, window]() {
+                if (window != m_lastWindow) {
+                    return;
+                }
+                if (auto *proxy = validICByWindow(window.data())) {
+                    cursorRectChanged();
+                }
+            },
+            Qt::QueuedConnection);
     }
 }