There's an odd thing with PXE imaging using MAC addresses. You have to specify them with 7 bytes.
MAC addresses are manufacturer assigned 6 byte numbers. The first 3 are assigned to identify the manufacturer, the last 3 used for uniqueness. A manufacturer can be assigned more than one 3 byte sequence of course.
So where does the seventh byte come from? The format of PXE MAC addresses are 01-xx-xx-xx-xx-xx-xx where the 01 stands for the version of ARP being used. It has never incremented to version 2.