adding a fixed length column to an existing table does not work correctly when the table is subsequently edited in access. other columns in the table seem to get wiped out.
more details here https://sourceforge.net/p/jackcess/discussion/456473/thread/db6a000575/?limit=25
got some time to look at this last night. think i figured some stuff out. hoping to get this sorted in the next few days.
this is fixed in trunk and will be in the 4.0.8 release