Sorry for my previous topic, it seems I didn't expose my problem like I should have.
Here it is:
After installing WPML 2.4.1, I noticed all the portfolio categories in the "Which categories should be used for the portfolio?" section of the Template Builder had disappeared.
The result of this is that every Portfolio I create (I have a "design" one and a "photography" one) now showcases ALL portfolio items, without filtering them.
I thought Nick's fix in this post ( http://www.kriesi.at/support/topic/latest-wpml-breaks-choices-portfolio-section ) was the way to go but now I even doubt the problem's the same.
Thank you in advance for your help.