What are the rules of combining different types of EU visas - specifically, the national and schengen visas for Spain.
A person doesn't want to break any rules, and he knows about the 90/180 rule. He has a 1 year schengen visa, and two student (Type D) visas, for the second and the fourth quarters of the year.
The result is that his months of living in Spain will look like this: 3 months schengen, 3 months student, 3 months schengen, 3 months student.
Theoretically, he does not violate anything. On the other hand, he lives the whole year in Spain and does not cross the borders.
Is this trick legal? What are the drawbacks and pitfalls?