In my American PBEM in the long 1775-1783 campaign, my militia/continental units have not been disbanding at the end of each year. Yet I am also playing a Montcalm PBEM and American militia are disbanding at the end of the year. So it seems the bug is scenario specific to the 1775-1783 scenario rather than a game wide bug.
Any idea if the problem is something simple that we, as players, can change in the scenario file to fix the problem ourselves?