How to export QT with transparent background in 6.2?

Hi, Folks.

I'm used to export videos with transparent background in earlier versions.
I've now updated to version 6.2 (first install after the version 6 release) and I can't export with transparent background.

I set the master page with no fill or I choose a color and set transparency to 0%.
The same I do with the actual normal page and I can't get the background transparent, only a black one.

Is it a bug or am I missing something?

Thanks,

Daniel