/maincontext/timeout-once randomly fails

At least on win32, I get about 30% of the time:

# /maincontext/timeout-once summary: Test g_timeout_add_once() works
Bail out! GLib:ERROR:../glib/tests/mainloop.c:2364:test_maincontext_timeout_once: assertion failed (counter == 1): (0 == 1)

I tried to do a while(g_main_context_iteration ()) that didn't help.