Deserializing merkleblock message
It seems that the transaction hash and the merkle root are both serialized in the gettxoutproof, but byte-wise reverse.
As stated in the bitcoin developer reference, 


  Bitcoin Core RPCs accept and return the byte-wise reverse of computed SHA-256 hash values.


So regarding your example, the hash (byte-wise)

81 48 74 0e ... 24 3c c4 a8


is contained twice in reverse in the gettxoutproof as:

a8 c4 3c 24 ... 0e 74 48 81


In this special case it is contained twice, of course, because with only one transaction the merkle root equals the according transaction hash.