First wl_surface_commit after unmapping doesn't trigger xdg_surface_configure

I'm working on an xdg-shell client which needs to hide/show its xdg_toplevel on demand.

I can hide just fine:

wl_surface_attach(wl_surface, NULL, 0, 0);
wl_surface_commit(wl_surface);

However, I'm struggling to show the toplevel back again. From the protocol doc (emphasis mine):

Unmapping an xdg_toplevel means that the surface cannot be shown by the compositor until it is explicitly mapped again. [...] The xdg_toplevel returns to the state it had right after xdg_surface.get_toplevel. The client can re-map the toplevel by perfoming a commit without any buffer attached, waiting for a configure event and handling it as usual (see xdg_surface description).

Therefore, I'm assuming I should just do this:

wl_surface_commit(wl_surface);

...and wait for xdg_surface_configure before attaching the buffer.

However, in Weston, the xdg_surface_configure event doesn't arrive after this.

OTOH, It is possible to show the toplevel by just attaching the buffer, without waiting for anything:

struct wl_buffer *wl_buffer = draw_frame();
wl_surface_attach(wl_surface, wl_buffer, 0, 0);
wl_surface_commit(wl_surface);

/*
 * This just works and triggers the xdg_surface_configure as well.
 * However, it violates the "commit without any buffer attached" rule.
 */

I compared the behavior in sway and it does trigger xdg_surface_configure after that initial commit without a buffer.

Perhaps I'm misunderstanding the expected behavior here. I'd appreciate some clarification if that's the case.

A minimal project to reproduce the behavior: https://github.com/czak/showhide

Thanks!