Leap Year

In the "Calendar" settings you will find a "leap year" setting, what is it used for?
The "Leap Year" setting is used to add a virtual/invisible Feb-29, also on non leap year.
(default is OFF)

The result is, that when there is repeating pattern in your shift planning, that there is a shift plannen on this virtual day, but IRL the Feb-29 does not exist in non leap year, so the shift will never take place.
The reason for this (strange setting), is that some companyes use it to fenerate their repeating patterns for their employees.