It was very odd I must admit, I did not have any real injury problems at all as you say, maybe I hit a glitch or just got lucky.
I played Ricardo at RW as neither Perez or Under performed that well, he was immense and bagged goals most games. I was using a formation someone created on an FM forum I am part of and it worked a treat.
I did make subs throughout matches so I can only think the best eleven screenshot provided only shows games players started not including substitutions, I definitely played some of the players from the bench more than it states above.
I think there are some things that need to be tweaked in game but we'll see how my 2nd season goes, if the injuries thing plays out the same way then I know there may be a glitch with my save