In taking my SoU character back through the SP campaign, I got Tomi poisoned. Resting usually cures this, but this time the sewrver said, "Secondary Poison Effect taking place." When we were through, his stats were changed, to a 21 STR and a 28 DEX. But, later, I used a Heal spell on him, and all of his stats went to 8/-1. Is this a bug?

Uhm, it's certainly not something that's supposed to happen, no. Poison lowers one of the ability scores instead of raising it, and removing poison should return everything to its normal level.
It actually sounds more like disease than poison from the lasting past a rest, but even so it's definately not right.
IIRC, Heal won't do this, you'd need a restoration spell to remove the decreased stat effect or a cure poison/remove disease spell to get rid of the actual poison/disease to stop it from doing more damage.
Talk to Aribeth and have her heal you, see if that helps. But be sure to hang on to an earlier save just in case.

Leggy, I used both a Restoration and Lesser Restoration. Same thing, and it's carrying over into Chapter 2. I think I'll restart, especially since I Levelled her to 19 in another module.