When validating dates JIRA rejects dates as invalid if the the date is the start date of daylight savings time daylight savings time transitions at midnight in the system's timezone.

Effected dates and timezones include the following in the year 2010:
Cannot parse "21/03/2010": Illegal instant due to time zone offset transition (America/Havana)
Cannot parse "17/10/2010": Illegal instant due to time zone offset transition (America/Asuncion)
Cannot parse "17/10/2010": Illegal instant due to time zone offset transition (America/Campo_Grande)
Cannot parse "17/10/2010": Illegal instant due to time zone offset transition (America/Cuiaba)
Cannot parse "10/10/2010": Illegal instant due to time zone offset transition (America/Santiago)
Cannot parse "10/10/2010": Illegal instant due to time zone offset transition (Antarctica/Palmer)
Cannot parse "10/10/2010": Illegal instant due to time zone offset transition (America/Santiago)
Cannot parse "17/10/2010": Illegal instant due to time zone offset transition (America/Argentina/Buenos_Aires)
Cannot parse "17/10/2010": Illegal instant due to time zone offset transition (America/Argentina/Cordoba)
Cannot parse "17/10/2010": Illegal instant due to time zone offset transition (America/Argentina/Tucuman)
Cannot parse "17/10/2010": Illegal instant due to time zone offset transition (America/Sao_Paulo)
Cannot parse "28/03/2010": Illegal instant due to time zone offset transition (America/Scoresbysund)
Cannot parse "28/03/2010": Illegal instant due to time zone offset transition (Atlantic/Azores)
Cannot parse "30/04/2010": Illegal instant due to time zone offset transition (Africa/Cairo)
Cannot parse "25/03/2010": Illegal instant due to time zone offset transition (Asia/Amman)
Cannot parse "28/03/2010": Illegal instant due to time zone offset transition (Asia/Beirut)
Cannot parse "02/04/2010": Illegal instant due to time zone offset transition (Asia/Damascus)
Cannot parse "01/04/2010": Illegal instant due to time zone offset transition (Asia/Gaza)
Cannot parse "30/04/2010": Illegal instant due to time zone offset transition (Africa/Cairo)
Cannot parse "22/03/2010": Illegal instant due to time zone offset transition (Asia/Tehran)
Cannot parse "01/04/1981": Illegal instant due to time zone offset transition (Europe/Minsk)

This is a direct result of the date being treated as a time with the time portion being set to 00:00:00. On the day of transition to daylight saving the times between 00:00:00 and 00:59:59 don't exist and so the date is rejected.