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It appears that the when you bring in a relief pitcher at a time when there is an existing count on the batter, the result is always credited to the relief pitcher. This should not be the case in all situations. The official rules (I've added them below) are such that there are various results depending on the count at the time of the switch as to who the AB is credited to. I've tried this with counts that should go both ways and it is always credited to the relief pitcher (positively or negatively).

Doc

(1) If, when pitchers are changed, the count is
2 balls, no strike,
2 balls, 1 strike,
3 balls, no strike,
3 balls, 1 strike,
3 balls, 2 strikes,

and the batter gets a base on balls, charge that batter and the base on balls to the preceding pitcher, not to the relief pitcher.

(2) Any other action by such batter, such as reaching base on a hit, an error, a fielder's choice, a force out, or being touched by a pitched ball, shall cause such a batter to be charged to the relief pitcher.

NOTE: The provisions of 10.18 (h) (2) shall not be construed as affecting or conflicting with the provisions of 10.18 (g).

(3) If, when pitchers are changed, the count is
2 balls, 2 strikes,
1 ball, 2 strikes,
1 ball, 1 strike,
1 ball, no strike,
no ball, 2 strikes,
no ball, 1 strike,

charge that batter and his actions to the relief pitcher.

(i) When pitchers are changed during an inning, the relief pitcher shall not have the benefit of previous chances for outs not accepted in determining earned runs.

Thanks sportsdoc. We are just finishing our testing of our next release, and this is not going to make it in. We will make sure it gets into the following release, and it will automatically fix itself for previously entered games and all stats will be updated