Atherton I've only had for a year but he's dropped 3 points in determination, in fairness both my team leaders were lower than him at about 8 and 13 determination but it feels a bit extreme.
Harkin has been here 2 years and dropped 2 points, the first year I'm not sure of the Team Leaders but in the second there was the 8 and 13 (same as above) but he still fell, so I'm guessing he liked the one that had 8.
Craig is a player who has slightly gone up, same Team Leaders as Harkin but it's strange that he's so slow compare to the steep drop of the others. I don't have too many players that increase as I usually focus on getting high determination players.
This season I've sold my 8 determination team leader and I'll post anything I notice from that (just started the season). I appreciate the answer back, I'm not positive it is a bug just trying to rule it out as it does seem more focused in reducing the attribute than increasing.