QAction tooltip does not show up when containing QMenu is torn off

I have attached some sample code based off the Menus example (https://doc.qt.io/qt-5/qtwidgets-mainwindows-menus-example.html, https://code.qt.io/cgit/qt/qtbase.git/tree/examples/widgets/mainwindows/menus?h=5.15), and cut it down. I have a menu containing a menu with a single action (Edit > Format > Bold). The Format menu can be torn off (with setTearOffEnabled), the Format menu has tooltips set to be visible, and the Bold action has a tooltip set ("bold").

If I navigate in the menu and hover the mouse over the Bold action / menu item, I see the tooltip. If I then tear off the Format menu so that it is in its own window, hovering over the Bold action in the torn off menu does NOT show the tooltip.

I would expect the tooltips to show on menu items whether or not the menu is torn off.

(pretty sure I'm compiling with Qt 5.10)