I have a date field, PayPeriod_EndDate, that is calculated based on another date field, PayPeriod_StartDate. For the start date, all dates are disabled, except for the 1st and 16th of any given month. If the selected start date is the 1st, the end date should be the 15th. If it's the 16th, the end date is the last date of the month. The calculation works until the form is saved as draft. When opening the draft the end date is always 12/30/1899. Here's the calculation on the end date:
=IF(DAY(PayPeriod_StartDate)<16, DATE(YEAR(PayPeriod_StartDate),MONTH(PayPeriod_StartDate),15), DATEVALUE(DATE(YEAR(PayPeriod_StartDate),MONTH(PayPeriod_StartDate)+1,1)-1))