Do you know how long ago this happened? I did notice a team in the CL semi-final last season got 20%. I was assuming it was because he had a GK as his MC, or Nordeus did a game update and accidentally bugged the formation.
however I've run the 4-3W-3 three times this season and it was legal on all occasions. Most recently I used it this past Friday (10/3) against a 4-4-2 classic in the cup.