Some subsurfaces change but are never committed

Another potential issue spotted while working OBS Studio's port to be a native Wayland client. Have a look at the attached screenshot.

There are lots of subsurfaces in this program, but there's this particular situation that involves 2 subsurfaces. Have a look in this snipped:

 [3445114.921] -> wl_compositor@4.create_surface(new id wl_surface@55)

...

[3445125.333] -> wl_subcompositor@12.get_subsurface(new id wl_subsurface@62, wl_surface@55, wl_surface@24)
[3445125.348] -> wl_subsurface@62.set_desync()

[3445125.353] -> wl_surface@55.set_buffer_scale(1)

[3445125.378] -> wl_subsurface@60.set_position(0, 0)
[3445125.386] -> wl_subsurface@61.set_position(0, 22)
[3445125.396] -> wl_subsurface@62.set_position(1006, 0)
[3445125.408] -> wl_surface@55.set_buffer_transform(0)
[3445125.414] -> wl_surface@55.commit()}} *//{{ ←←←←← This is the first and only commit of wl_surface@55}}

[3447948.021] -> wl_subsurface@62.set_position(1006, 0)

[3448025.196] -> wl_subsurface@62.set_position(1014, 0)

...

The full log can be found here: obs wayland debug.txt

As you can see, wl_subsurface@62 (subsurface object of wl_surface@55) has many calls to set_position(), but they are never committed. This surface has no buffer.