waylandsink: "gst-launch-1.0 videotestsrc ! waylandsink" results in "xdg_surface has never been configured" error

I wasn't able to get "gst-launch-1.0 videotestsrc ! waylandsink" working when waylandsink is using XDG-shell protocol: it stalls at "Setting pipeline to PLAYING ..." with the xdg_surface@15: error 3: xdg_surface has never been configured error message (from weston), no waylandsink window is shown on the screen.

I am using gst-plugins-bad at commit 4430fa0e (master branch as of March 11; there were no changes to waylandsink after that) and weston-5.0.92.

Attached is the file with console log followed by the gdb log when the command is run from gdb: there are two calls to gst_wl_shm_memory_construct_wl_buffer(), the call chain being ...->gst_base_sink_do_preroll()->gst_wayland_sink_show_frame()->...->gst_wl_shm_memory_construct_wl_buffer(). This didn't get into the log, but I tried setting breakpoints at handle_xdg_toplevel_configure() and handle_xdg_surface_configure(), and none of them was hit before the "xdg_surface has never been configured" error happened.