Merry Christmas!
There are two more things that I found.
1) When you put skill points in Buskfyr's strength upgrade and it evolves into Buskfyrael, the skill points are lost as the skill in that slot changes and the points are not returned to be usable nor stay in the new skill. This didn't happen to the other skill (ability) that changes when I observed it.
2) Speed's effects don't change with battle buffs/debuffs nor with items. So what happens is only base speed matters, but changing someone's speed does nothing.