This is the boot code version number. I think it is not supposed to be at that location. See optiboot.c and the Makefile: the version is meant to be in a section named "version".
All targets in the optiboot makefile that do not specify -DBIGBOOT have an option like this in the LDSECTIONS variable:
-Wl,--section-start=.text=0x7e00 -Wl,--section-start=.version=0x7ffe
which makes the version section start 2 bytes before the end of the 512 byte range in which the bootloader should fit.
For some reason the big bootloaders do not have this option.
I added such an option for the atmega1284:
atmega1284: LDSECTIONS = -Wl,--section-start=.text=0x1fc00 -Wl,--section-start=.version=0x1fffe
(version section starts at the end of the 1024 bytes in which the big bootloader should fit)
If I make the bootloader again, the version number ends up nicely at address 1FFFE and the hex file looks like this:
:020000021000EC
:10FC0000112484B714BE81FFF3D085E08093810076
...
:10FDE0001F93182FE3DF1150E9F7F2DF1F910895F9
:0AFDF00080E0E8DFEE27FF2709940A
:02FFFE000504F8
:040000031000FC00ED
:00000001FF
(I did not post the complete hex as all byte are different from the original hex file and I have no 1284 to test this)