Lock ID "M" records created in Interim Workbench - why?

Greetings!

We had an issue yesterday where payroll entered interim entries in the Interim Workbench (US) but some did not display in the Revise/Review screen. Upon researching, some of the transactions had an "I" Lock ID code in the Individual Time Entry screen and the ones not displaying had an "M". All of the records were in the F06116. We were not using the Interim Timecard Generator so we could not determine why the "M" records were created. The p.o. in the Interim Workbench pointed to the Timecard MBF (P050002A) that did not have the Batch setting. We had to delete the "M" timecards, deleted all the other interim entries and re-enter them into the Interim Workbench - then everything worked as expected in that all records were "I" records and were subsequently processed in payroll. We were unable to recreate this scenario. Very weird!