Not quite true!
The wing came of that DR400 because the pilot was doing aerobatics that the aircraft is not cleared for , during the investigation it was found by the french authoritys that the glued surface area of the spar booms was able to take the design loads but only if the glue joint was of a very high quality.
This is usualy not a problem as almost all of what Robin turn out of the factory is very good ( the build quality was commented upon faourably by the UK AAIB in the report when a DR400 broke up in flight following striking an object after landing on a previous flight ) but it was felt that a small increase in the glued area of the spar boom would increase the margin for error at manufacture and garantee the structure would not fail even if the glue joint was not 100%.
An AD has been issued that requiers the spar boom to have some aditonal wood glued onto the spar , the cost of this is about £3000 so if you are looking at buying a DR400 cost this in to the price that pay !.
A few aircraft around the S/N 770 range are exempt from this requirment.