I have the same feeling with defenders.

Every time I sub a defender I concede a goal shortly after. Its not like I'm playing with one less defender either, I swap a DC for another DC, or a DL for another DL, but time and time again, once a defender gets subbed I seem to concede.

It happens so often and so frequently for it to not be a coincidence in my opinion. I've come to the conclusion that its another one of those game bugs, like the double corner and overly frequent troll results.

Its something that does spoil the game, as it means unless I am 4/5/6 goals up I NEVER sub a defender unless they get injured out of fear of conceding.