Distorted weight parts after rendering

Hi had problem with a preliminary test pose on a wip model for my client.
this how it appear in preview window:

and this is how appear after rendering (pressing f12 key) and turn back to 2d window (or preview rendering window), also is the after reload the saved (not deformed by rendering) file:

the two gun are totally distorted. The model is rigged with rigify and posed.

Any solution for this?

Jholen, maybe the problem is that your version of Blender has some bugs. Install an earlier version and try again to make the render. I hope I’ve been helpful.

Hi Tacos77, thanks for your reply,
I have 2.71, maybe a bug? Unfortunately cannot share the original file (is a commissioned work).
The strange is when before start the rendering is all ok, start rendering and mesh is distorted, crtl+z turn back at the original (correct) status.