This is a truly ugly bug.  I have opened Bug Track #559 for this.
   https://www.cinelerra-gg.org/bugtracker/view.php?id=559
which includes a donation of US $100 for a good fix -- only payable to a PayPal account.

On Tue, Mar 9, 2021 at 12:54 PM Camille Harang via Cin <cin@lists.cinelerra-gg.org> wrote:
Hi Igor, thanks for the reply and for validating the bug. I tried your
workaround, indeed it looks better in some cases, the black dissapears
of course, but the alpha gradients on PNGs and anti-aliasing on text are
lost…

Thank you!

Camille.

Le 09/03/2021 à 10:06, Igor BEGHETTO via Cin a écrit :
> Hi to all!
>
> I confirm the bug reported by Camille.
> Here two videos about Title effect and Image with Dissolve Transition:
> https://streamable.com/86y59m
> https://streamable.com/ywcaee
>
> This is my trick to solve it:
> https://streamable.com/vkp9ou
>
> IgorBeg
>
>
> PS:
> Cin_release I am using: Ub16_20201031_static
> Sorry I have not try the last AppImage for older distribution.


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