Cant use Large thumbnail size above 600 x 400 px

Hey guys!

After I switched my large thumb size from 828 to 1656px and regenerated all thumbs I cant add my Large image to post with 1656 size. When I adding my picture I can only select Large size with 600px width. Btw, I got NO such thumb size as 600px anywhere. And I cant figure our what this value is about. All my thumbs files are good and corresponding to my options sizes.

And when I attach that large picture i got correct 1656px image but with 600×400 style.

Please help, it makes me really crazy!

P.S. problem still occurs with no plugins and def theme.

Thanks!