regardless of their cover.
And where exactly did you get that? O_o
This is the description of the spell in the pen and paper version of D&D 5ed
https://roll20.net/compendium/dnd5e/Magic%20Missile#contentMagic missile have been working like this since D&D first edition. For the people who enjoy discussiong rules, this is a "non issue". They all agree on that definition. You can read the excelent analysis by Niara on the spells. That is why a shield spell that specifically counters magic missile is so handy. And why there are shield amulets that create the protection without the spell.
Also, why wizards pay attention to things like the kind of salvation their spells, provide, resistances, etc. It is part of the game.
