Data statement and pbp3

I am using a pic18f43k22. I use a single data 1 statement to initialise byte zero of the EEPROM.
When I read back the EEPROM after programming the chip byte 0 is correct but byte 1 has been cleared as well. Does anyone have any idea why this second EEPROM byte has been cleared?

Graham

When programming the chip, programmers write WORDS, even to the byte sized internal EEPROM.

If an even number location is specified in DATA or EEPROM, the odd numbered location will be cleared if not also specified.