One is probably a mirror? Try using this and seeing what happens.
if (nRet == 0) {
SekMapHandler(4, 0x200000, 0x2FFFFF, SM_RAM);
SekSetWriteWordHandler(4, neocdWriteWord);
SekSetWriteByteHandler(4, neocdWriteByte);
SekSetReadWordHandler(4, neocdReadWord);
SekSetReadByteHandler(4, neocdReadByte);
SekMapHandler(5, 0xE00000, 0xFFFFFF, SM_RAM);
SekSetWriteWordHandler(5, neocdWriteWord);
SekSetWriteByteHandler(5, neocdWriteByte);
SekSetReadWordHandler(5, neocdReadWord);
SekSetReadByteHandler(5, neocdReadByte);
}