Introduced in version 18.104.22.168
If you move the printing fields (up or down) in the Printing Fields options page and click on OK the new order is not saved. This issue is fixed in this version.
If you are using a version of One Stop Order Processing before this version (22.214.171.124) you can resolve the problem (i.e. save the new order of the printing fields) by clicking on the Edit button after moving the field and then clicking on OK (in the Printing Field dialog). When you then click on OK in the Options dialog the new order is saved.