I added a holiday in the schedule, with a repeat option of "once", which it accepted, created another with a different name and date, but it claims an entry already exists, which it doesn't, if I change the repeat to anything other than "once", then it saves no problem.

If I had to guess, the repeats value "never" in ost_schedule_entry is what is triggering the assumed duplication.

p.s. there's no Tag for 1.14.0-rc2 (or any 1.14 version for that matter that I can see).