I just completed EoB 1 and transferred my save game to the sequel and had an odd bug happen - all of my party's stats were increased by 10, leaving most of their stats in the mid-high 20s. So my level 7/8 party is sitting with around 250 HP a piece and deals 30-odd damage with each melee hit. What did I do wrong, and how can I fix it?

Weird. Have you tried simply transferring again?

If you are feeling adventurous, you could always just manually hex edit all the stats to restore them to what they should be. I tinkered with hex editing Eye of the Beholder (first game) back in the day and it worked just fine. But I realize that option isn't for everyone since it requires knowing how or learning how.