But this struck me like a complete ignorant, man. I had no stroked objects in the artwork, everything expanded and "good to go" (like always). I knew that Illustrator saved the "file library" symbols within the file (even if the symbols were never used in the artwork), but I had no clue it did the same with brushes (at least not unused ones). I had around 20 grunge splatter brushes in the file library and "boom": all were saved along the empty canvas;) 5MB of never used brushes;)
p.s.: Damn, now I can only imagine how many works of mine were sold with a beautiful collection of brushes and symbols free, completely free of charge. Call me Mr. Charity;))