A funny UI problem is fixed. Now even if you type "17/7/7" in the begin or end date column (that is, one-digit year) it will be recognized as "17/07/2007".
But what if your project really dates from the beginning of Anno Domini? No problems, just create only one task from that period typing its date without missing zeros: "17/07/0007"
and GanttProject will stop adding 2000 to your one-digit year. If your project start date is not around year 2000 then one-digit year is interpreted literally, as 0007.