X11 event handling oddity?

While digging around in the mysteries that is X11 events handling with
DEBUG_XEVENTS enabled, I was getting a chunk of “Unhandled event 28”.
After looking it up, it seems like it is a PropertyNotify event. Now,
I was wondering, why are we getting it, since Xlib uses a strictly
subscription-based event notification?

Turns out SDL asks for it (in SDL_x11video.c, function
create_aux_windows). Any reason in asking for an event that is not
event recognized?–