Rad Racer 2 is indeed special, according to
http://wiki.nesdev.com/w/index.php/INESFlags 6
76543210
||||||||
||||+||+- 0xx0: vertical arrangement/horizontal mirroring (CIRAM A10 = PPU A11)
|||| || 0xx1: horizontal arrangement/vertical mirroring (CIRAM A10 = PPU A10)
|||| || 1xxx: four-screen VRAM
|||| |+-- 1: SRAM in CPU $6000-$7FFF, if present, is battery backed
|||| +--- 1: 512-byte trainer at $7000-$71FF (stored before PRG data)
++++----- Lower nybble of mapper number
Some mappers, such as MMC1, MMC3, and AxROM, can control nametable mirroring. They ignore bit 0.
On the other hand, if bit 3 is true, the cart has 4 KiB of RAM at PPU $2000-$2FFF, and it ignores the mapper's CIRAM A10 output (as in Rad Racer 2). One exception is #218, which uses the four-screen bit to switch between one-screen and V/H mirroring.