I'm not sure if this is a bug but it doesn't make sense to me.
In the year 2030, Serbia joins the EU, and the rule regarding the number of foreign players changes. From that moment on, a team cannot have more than 4 foreign players in total, including both the starting 11 and the substitutes' bench. Prior to Serbia's accession to the EU, I could not have more than 4 foreign players in the starting 11, while on the bench, I could have as many foreign players as I wanted.