BuildLegend and gPad

Dear ROOTers,

     I recently found a strange error moving from 530 to 532/533 release of ROOT.
It concerns the method "BuildLegend" (very useful!). The following code worked well in the previous release [1], while it doesn't in the 532/533.
The error I get is:

    Error: Can't call TVirtualPad::BuildLegend() in current scope     (tmpfile):1:

With a minor change of the code [2] it worked, but I cannot figure out why the code [1] doesn't work.
It seems that it is related to "gPad".

Thanks,

     Andrea

[1]

      TH1F h1("h1","h1",100,-2,2);
      TH1F h2("h2","h2",100,-2,2);

      h1->FillRandom("gaus",10000);
      h2->FillRandom("gaus",10000);

      h1->SetLineColor(kRed);
      h2->SetLineColor(kBlue);

      TCanvas* cc = new TCanvas ("cc","cc",400,400);
      h1->Draw();
      h2->Draw("same");

      TLegend* leg = gPad->BuildLegend();
      leg->SetFillColor(kWhite);
      gPad->SetGrid();

[2]

      TH1F h1("h1","h1",100,-2,2);
      TH1F h2("h2","h2",100,-2,2);

      h1->FillRandom("gaus",10000);
      h2->FillRandom("gaus",10000);

      h1->SetLineColor(kRed);
      h2->SetLineColor(kBlue);

      TCanvas* cc = new TCanvas ("cc","cc",400,400);
      h1->Draw();
      h2->Draw("same");

      TLegend* leg = cc->BuildLegend();
      leg->SetFillColor(kWhite);
      cc->SetGrid();