My b2evolution Version: Not Entered

Every time I click on "Write" link in evobar I get

Please enter a valid issue date

This happens since I upgraded my 2.4.5 blog to 3.3.1, upgrade to 4.0.0000-alpha didn't help either so it's something in my files/DB

The date field displayed cropped values like 05/04/200 in 3.3.1
After upgrade to 4.0 I get 1969-12-31 19:00 all the time

I can't figure out what might cause this. All dates in Tools > System are fine.
Date is OK too if I edit an existing post.

No hacked files [u]at all[/u]