Date format pattern mapping is incorrect in method InputUtil.MapDateFormatShortCuts:

case "y":
          return dateTimeFormatInfo.MonthDayPattern;
case "Y":
          return dateTimeFormatInfo.MonthDayPattern;

instead of:

case "y":
          return dateTimeFormatInfo.YearMonthPattern;
case "Y":
          return dateTimeFormatInfo.YearMonthPattern;

according to "Standard Date and Time Format Strings" from 
https://msdn.microsoft.com/en-us/library/az4se3k1(v=vs.110).aspx