Available for national team...or not?

I am becoming very frustrated with this. I am managing Italy U20, and when I select national pool, and apply filter 'available for U20' I should supposedly get the list of all players that I can move to U20 team. The problem is that some of these players (that are closer to age of 20 than 19) in fact can not be selected for matches. When I am asked to confirm squad for upcoming match, I have to remove them from selection.

Here is one example of such behaviour.