Why is everybody considering retrained units with high experienced a bug? What about all those veterans who can be called upon to join the army? Since there is no ability to disband experienced units and regain them later, with the same grade of experience of course, and it makes actually no sense at all to disband units, because one can´t recruit a full, or at least a half army, within short period of time ( at least not from once settlement, a capital perhaps, that in case of Romans, for example, is the only historical way till the granted citizenship to other italic towns, i see no bug in this at all. Old veterans from the previous campaigns are, of course, joining other veterans, while fresh recruits are mustered in new units.