Bug reported by Francesco Poli on the Debian BTS recently. Occurs with 7.0.3, on i965 (not reproduced with any other driver so far), with the "mayavi2" program. He says:

"I've seen the issue happen with basically any data source.
The test case I prepared is based on a simple (legacy) VTK data
file ('fakehurr_merid.vtk') generated by a Fortran program
('gen_fakehurr.f').

  $ tar xzf mayavi2-interpolation-bug-test.tar.gz
  $ ls
  fakehurr_merid.vtk  gen_fakehurr.f  mayavi2-interpolation-bug-test.tar.gz
  $ mayavi2 -d fakehurr_merid.vtk

The main window shows up, with a data source already loaded.

 * for menus, select Visualize -> Modules -> Surface
 * in the MayaVi pane, double-click on Surface
 * in the dialog window, check Interpolate scalars before mapping
 * click on the OK button

A nice visualization is shown, with very smooth colored areas.

 * in the TVTK Scene 1 pane, click on the Obtain an isometric view button

There's an area on the left where the interpolation seems to produce
a strange fake transparency effect (as shown in the attached PNG image).
Disabling the interpolation makes this defect vanish (but produces a
less convincing visualization)."

His tarball is available at:
http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=mayavi2-interpolation-bug-test.tar.gz;att=1;bug=478960

And the screenshot is at"
http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=foo.png;att=2;bug=478960

There's another similar report with mayavi2 on i965 but I can't be 100% sure it's the same problem:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=478880