TLegend : strange line appears in the saved .gif

Hello,

i tried to make a TLegend's box to be invisible with the macro below.

While indeed, on the screen when launching the macro, the legend has not a box as contour, in the saved .gif file, there is. Would there be a way to make this "box" to disappear in the saved .gif ? (attached file)
i mean my goal would be to make the big contour line around the legend+"The explanation" to disappear

thanks

{//used root 5.27/06

   gROOT->SetStyle("Plain");
   gStyle->SetPalette(1);

   TCanvas *c1=new TCanvas("c1", "A canvas", 10,0, 800, 600);    c1->SetLogy();

   histo_dummy=c1->DrawFrame(0,1e-4,27,10);

   TF1 expontential("expontential","exp(-x)",0,14);    expontential.Draw("same");

   TLegend legend(0.3,0.45,0.8,0.75);

   legend.SetBorderSize(0);
   legend.SetFillColor(kWhite);
   legend.SetFillStyle(1);
   legend.AddEntry("expontential","the explanation","f");
   legend.Draw();

   c1->SaveAs("test.gif");
}