Could this be a background-color bug in GTK+3.22?

[Jonas Camillus Jeppesen <jonascj sdu dk>]

(x-post from gtk-app-devel-list gnome org, not sure which one was
the proper gtk-list for this "user question")

Dear all,

I'm a user of the document viewer Zathura 
(https://pwmt.org/projects/zathura/) which uses GTK+ for its interface

Since upgrading to GTK+ 3.22 it has suffered from a background color 
bug/issue. The developers are not
giving this high priority (which is fair enough) so I'm trying to 
investigate it. Now asking your mailing list for input.
Please bear with me as I'm not GTK+ developer.

This video/gif demonstrates the issue: http://i.imgur.com/xcCgB03.mp4

What you see is this:

# 1. Zathura on the left with no document open, running in debug mode 
with GTK+ Inspector open on the top right.
The background is green because I've specified 'default-bg' as "green" 
in a config file and the application has this CSS rule:
> #@session@ * {
>     color: @default-fg@;
>     background-color: @default-bg@;
>     background-image: none;
> }

#2: I turn the background brown by specifying "* { background: brown; }" 
in the interactive debuggers CSS tab.

#3: Then a pdf file is opened and zoomed until it overflows the top and 
bottom of the window. This cause the window
background to turn black, and when I zoom out again the background stays 
black.

#4: I change the CSS specification in the interactive debugger and the 
background color reappears as it is intended.
I assume this triggers a reload/reapplication of the CSS.


Could that be a GTK bug? It appears as a rendering issue. When the 
background appears black GTK+ Inspector reports
the 'background-color' property as green or brown as I specified, not 
black as is displayed/rendered.

I'm afraid I don't have a minimal working example reproducing the 
problem. I would just like your input on whether it could be
a GTK bug or not.


Thank you for your input!

/ Jonas

P.S. Should anyone be interested in the application's code or CSS it is 
available here:
git clone https://git.pwmt.org/pwmt/girara.git
git clone https://git.pwmt.org/pwmt/zathura.git