Our firm has been using ProSeries for more than a decade.  I've seen it happen this year for various types of new K-1s added to clients with an existing list of K-1's.  Now, I'm working on a file that has Schedules A, B C, D, E, E2 and 15 K-1s with active related forms to each.  At the very bottom of Forms In Use, Form 1098, Sch B, Sch C with related 4562, 8829 and Asset entry items.  All at the very bottom of the Forms In Use - Forms Bar.  All else seems to be ordered as expected.  We are on a "stand alone" setup.

I've seen this issue occur in a Quickbooks chart of accounts setup.  And in QB, you can always resort the order by alpha or numeric order.  But no such resorting tool seems available and Revert to Default does nothing.  Hopefully this additional information helps if someone at ProSeries takes the time to troubleshoot this issue.