From the manual, p. 158:

The Address size sent (byte or word) is determined by the size of the variable that is used. If a byte-sized variable is used for the Address, an 8-bit address is sent. If a word-sized variable is used, a 16-bit address is sent. Be sure to use the proper sized variable for the device you wish to communicate with. Constants should not be used for the Address as the size can vary dependent on the size of the constant. Also, expressions should not be used as they can cause an improper Address size to be sent.