Hi
You can't fade to black and still have the lower track visible.and it's not a bug. A Fade out is usual for any text as the background is transparent and the lower tracks are not affected. They would be visible throughout.The text just fades away.
Fading to "black"means that there must be a black clip to fade to if the text remains on a transparent background. This black clip will naturally obscure the underlying track.
It would be possible to set your text editor to Full background (black) and then use the Fade through black effect, The text would fade to black and then cut to the lower track.
Alternatively set the text on its normal transparent background (when the lower track will be visible) and then add the Fade thru black effect. This is probably the closest you will get, but fading text to black MUST affect the visibility of the lower track.
Nat