So when Brigadier Grierson 5-2-3 (+1 defensive through experience)

got his letter of approval for promotion I checked the handy Union Generals list to see what his status is. it says he starts at 5-2-2, can be promoted to Maj. Gen. 5-2-2, but not higher. So I jumped at the opportunity.
But after his promotion he has dropped in quality anyway.

I thought that generals keep their experience gains when being promoted, baring changes due to being promoted above their abilities as in the examples above.
Is this normal?