Found the cause of the problem, it's due to the ray bias options that tries to avoid bad ray traced shadows.
http://www.blender.org/development/release-logs/blender-234/misc-improvements/

It's a bit late to fix this for 2.67, but the workaround is to go into the material and disable Auto Ray Bias (optionally you can set a manual value if there are artifacts).

Thank you so much, super service!!!

have a good week.

JF

I'm making other test that I did not think about before, and yes disabling auto ray bias stops that,

but I made a test without hair and auto ray bias enable and it has stop, so the bug might be related to the hair.

At the moment of writing I'm trying to see if its because I have activated hair dynamics.

For:

http://www.blender.org/development/release-logs/blender-234/misc-improvements/

I was not using Phong for specula, , I was using diffuse:Lambert and specular : CookTorr

I can now confirm that it happens only when hair dynamics is on.

Do I need to create another post?

No, it's not needed to open another report. Rendering without the hair indeed avoids the problem, the bug happens due to the hair influencing this auto ray bias. But I have to investigate what the proper solution is, if hair should be excluded entirely from this or if it still needs to be taken into account.

It only happens if I activate the dynamics (movements),

But if its just hair particles its ok,

Thanks a lot

JF

Fix in svn now, thanks for the report.

No problems, glad I could help,

Keep on the good work!!!

JF