I'm not suggesting Bernardo is ill-disciplined tactically, he's genuinely the last guy I'd expect to do that. My point is that playing in the most demanding position in the most tactically, technically, mentally and possibly physically demanding team in the world is extremely difficult and takes a long time to adjust to. I'd like to clear that I think he's been excellent this year (and still is, albeit more mutedly) and I believe he's actually improved in this positional means, but I just think he's not 100% developed in the role and it shows in the fact he occasionally drifts a bit to the right.
It's like all our other players, if they do something wrong like make a bad pass or get caught out of position you know it's not what Pep would've wanted them to do, but they do it anyway. Football's extremely difficult at this level and maintaining 100% concentration on everything must be extremely tough, and in the heat of the moment players sometimes get things a bit amiss.
What I consider to be a slight deficiency in Bernardo's game is also something I consider to have been eliminated by the very latest next season's end. By which point I expect him to be one of the outright best midfielders in the world because the rest of his game is already close to world-class. Maybe not his heading, but everything else.