I found that installing subtitlecomposer changes the mime database so that the type of two png files from the default Ambiance theme becomes "text/x-tmplayer" instead of "image/png", thus gtk-window-decorator unable to load the theme.
I found that installing subtitlecomposer changes the mime database so that the type of two png files from the default Ambiance theme becomes "text/x-tmplayer" instead of "image/png", thus gtk-window- decorator unable to load the theme.