Is CRC32 additive?

On several places I've read that crc32 is additive and so: CRC(A xor B) = CRC(A) xor CRC(B).

The above statement was disproven by the following code I wrote:

import zlib
def crc32(data):
        return zlib.crc32(data) & 0xffffffff

print crc32(chr(ord("A") ^ ord("B")))
print crc32("A") ^ crc32("B")

Program output:

1259060791
2567524794

Could someone provide a proper code proving this theory or point me where I've failed?