Category field is not saved

It seems like values from selects fields are not saved correctly in the session object or maybe they are just not displayed right when you come back to the page.

I assigned a node to two categories, put some text and went to add an image with "Add new" button. Everything went well just that when I posted the image and got back to the original node I was posting, the selected categories were not preserved (other value were ok). Instead the first one was selected which is a default (for required select list).

Was I clear enough?