Creating terms at levels deeper than the max_levels setting does not work

I have a typical vocabulary with hierarchical levels: continents > countries > regions.

As the number of continents and countries are fixed, there is only the need to add new terms to the regions. Unfortunately when I try to create a new term for the regions, the box for the new term pops up and I can fill it in, but after clicking "create" the term is not there. The new term is also not present in the terms list at categories, so it is not created/saved.

For the first two levels, continents and countries, its works to create new terms.