Well, I downloaded some Background GFX from here, and some of them uses MAP16 page 42. And now MAP16 page 42, 52, 62 and 72 has been used.
I downloaded a new background, but it's uses MAP16 page 42.
How to change MAP16 page quickly that backgrounds used?
2019 Edit: Use Lunar Magic's background & MAP16 remapping feature to solve this problem