Transparency does not work for .tex output

Transparent pads are not working correctly when saving a canvas as .tex. Instead, a black background is created. I found these three lines in the .tex output responsible for this black background:

\definecolor

Unknown macro: {c}

Unknown macro: {rgb}

Unknown macro: {1,1,1}

;
\draw [pattern=, pattern color=c] (0,0) rectangle (20,13.5632);
\draw [pattern=, pattern color=c] (0,0) rectangle (20,13.5632);

Removing them solves the problem. Is it possible to avoid writing these lines when calling the SaveAs function, if it detects that it is a transparent pad?

See further details in https://root.cern.ch/phpBB3/viewtopic.php?f=3&t=1875&start=15#p82127
Thanks.