This type of design is commonly used for built-up members used in buildings and bridges. I was mildly surprized 6 years ago when I did my first bridge inspection, and noticed all of the girders had single pass fillet welds (of minimal size) on one side of the joint. This bridge has withstood numerous CA earthquakes. Many built up trusses are detailed and fabricated with this detail as well.

I have never seen one that has failed either. I was told by one Engineer several years ago (on his specific project) they are "ductile primary members." I am curious as to your consultants basis for the query. Try contacting www.aisc.org. Please post a response when you get one.