I'm another who would like to know why.
I certainly do not see it as a illegal formation.
Why? because on two occasions in the group CL matches I countered a formation with three players on one side against a asymmetric formation.
Won both games and no possession loss.
It's time the basic requirements for complying with what is deemed to be legal or illegal formations are made clear for all.
How can you play a game fairly with out rules.
A missed opportunity the other week when we had the Q&A with the developers. doubt we would have got the answer though.