The part is only 64 bytes. According to the data sheet:

The RTC registers are located in address locations 00h to 07h. The RAM registers are located in address locations 08h to 3Fh. During a multibyte access, when the address pointer reaches 3Fh, the end of RAM space, it wraps around to location 00h, the beginning of the clock space.

Which is why you see what you see when you try to access data greater that 64 bytes (0x3F).