If a new calendar block specifies a repeat that overlaps an existing appointment, changing the repeat to No Repeat doesn't immediately reset the repeat state.
1. create an appointment on 31/12/16.
2. create a calendar block on the 24/12/16, with a Weekly repeat, set to repeat Once
3. click Apply. A 'Cannot schedule Calendar Block' message should be displayed, listing an overlap of the appointment
4. change the Repeat to No Repeat
5. click Apply. The same message will be displayed, despite there being no overlap