Take a look at the order id settings and the handling of order id's, their might be some problems with the order id settings. If they for example are set on a module/delta and then deleted again, will the corresponding record not be deleted from the order_id database table. This gives some problems.

Furthermore should the user do an action before the order id settings are saved, right now are they saved no matter what if the other settings are saved.

Finally should their be made some checks when the order id settings are saved. For example that we don't have a transaction in the db with the same order id or an order id near to the one set.