Problem of text quality

Hello,

I’m not a shotcut expert, but there’s something I don’t understand about adding text to a video.
I get a drop in text quality when there’s no video in a track above it.

Here’s a capture of the text during the video and when there’s only text.

The only solution I’ve found to keep good quality is to add a black image after my video.

have you ever encountered this problem or is there something I’m doing wrong?

thank you for your help

This is normal because the anti aliasing is in the alpha channel, and a video clip on the bottom video track does not blend with anything.

Thanks for your quick answer, but what is the best practice in this case ?

Change the background color from transparent to something opaque in Properties.