Hi Thomaso and Pšenda
Yes matte is set with the red line through it, strike out.
It happens sometimes and not others. It seems random. It happens off and on with saving them to a folder, and most of the time uploading to web pages. Uploading to web, even on ewhich has saved in my puter folders with trans background can at times upload with a black one to the web-page.
If I upload them into a game, they have their transparency even if with black backgrounds.
I had advice elsewhere a few times, i need an alpha chan on it.
Thanks very much for trying