You would also need to change the cast in line 919 in sharededb.cpp
Code:
item.StackSize = (uint8)atoi(row[ItemField::stacksize]);
There may be other places, but that one was obvious.
Like I said earlier, the reason you see 244 is that you have it set to 500 in the database and 500 % 256 = 244. If it was 600 in the DB you'd see 88 in game, and if it was 400 in the DB you'd see 144 in game. Nothing unusual about it, just a number being truncated to fit a variable.