Backdrop change causes "say" missing

backdrop-say.xbp.zip

onStart => {

	say "故事开端：蜗牛爷爷在给小蜗牛们讲自己年轻时的故事，说自己见过广阔无际的大海", 1

	setBackdrop "山川"
	say "Hi"
}

With setBackdrop "山川", the "Hi" is missing.

If we remove setBackdrop "山川", the "Hi" is visible.