QMenu breaks when removing last action

When the last QAction is being removed the QMenu renders the string "Activate". Subsequently added actions are no shown anymore (while the QMenu API still reports the correct actions).

I have create a minimal example which demonstrates the problem: https://gist.github.com/dirk-thomas/ad2df445e150c0a3545a357ef3da806c
After building it use the two command action to append / pop actions to the second menu. After appending once and popping once the list menu is not empty but show the mentioned string. Afterwards appending further actions are not rendered in the list menu anymore.