Summary of the steps to reproduce (from QA tester of our application):
1. click into the year field - it seems not possible to change the year, however:
2. press 1 and a date of 10000 is entered
3. press 2 and it's 20000
4. press 3 and it's 30000 (if you press 3 first, it could be 3000 and so it would be valid)
5. you get a error message e.g. Invalid year: 10000
6. nevertheless you can change the year with the arrow keys/buttons but for every change you get the error message.
You also get the error message if you go to the upper and lower bounds of the calender, which is the year 1582 and 10000 (both exclusive) by means of arrow keys / arrow buttons. You can change the year into the wrong direction if you are willing to confirm the error message on every keypress. And if you want to change the year back to some meaningful value, you have to confirm the error message again, until you hit a valid year. If in such a invalid year (e.g 1580), you can click on a day and the date will change to that date in 1583.