The support replied to me that this behavior is as designed:
"A published c3di file is saved as PVZ file, an illustration can contain 2D, 3D figures, when you publish an illustation, you can export one or more of the figures in one or more of these formats, including 3D Creo View model, image and 2D illustration. But publishing c3di file as PVZ is only for 3D figures, if c3di file only contain 2D figures or you only need publish 2D figures, you do not need the function of Publish, File>Save Figure as has been able to meet our needs."
Then this functionality at the moment is for me useless because I need svg files in pvz on publish to use them in Windchill. Actually I have this functionality automatically on checkin from Illustrate, I can't think to manually save svg locally and upload them as secondary content in Windchill.
I suppose that it can be useful but in a publish workflow, like 3d publish.
I tested also the Creo View Adapter for Illustrate and doesn't work (in 7.1) with c3di made with 2D publish option.