WS410 API _size parameter not always working

According to the documentation the /ws410/rest API should support a <collection>_size parameter to limit the number of records returned.

This works and returns 2 records:

http://localhost/ws410/rest/users?users_size=2

This does not work and returns all records (thousands):

http://localhost/ws410/rest/medias/?medias_size=2

Why does it not work for medias?