Interesting. Found on the internet?
I've also found reference to a T46 bodied by Ferdinand Keibl, but it could be a typo. There is a T49 roadster, also without running boards, which seems to be unambiguously attributed to Erdmann & Rossi (chassis 49424).
The Bugatti Register makes mention that the car in question appeared at Schloss Bensberg Classics 2009, but that car is actually chassis 49377, bodied by Gangloff: