IEEE P1619/XTS, inconsistent reference implementation and test vectors
From §5.1 ‘Data units and tweaks’, p. 4:


  Each data unit is assigned a tweak value which is a non-negative integer. The tweak values are assigned consecutively, starting from an arbitrary non-negative integer.  When encrypting tweak value using AES, the tweak is first converted into a little-endian byte array.  For example, tweak value 123456789A16 corresponds to byte array 9a16, 7816, 5616, 3416, 1216.


The test vectors appear to be written as byte arrays, not as integers (which in English are written big-endian), so where it says


  Data unit sequence number 9a78563412


on p. 23, that presumably means the integer 0x123456789a, i.e. 78187493530 in decimal.