A gpart(8) mystery on 10.3-RELEASE

[Trond Endrestøl]

What am I doing wrong? Can't gpart(8) write both the pmbr and the efi 
image as a single command? Is it an off-by-one error in gpart(8)?

uname -a
FreeBSD  10.3-RELEASE FreeBSD 10.3-RELEASE #0 r297264: Fri Mar 25 02:10:02 UTC 2016     root at releng1.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC  amd64

gpart create -s gpt ada0
ada0 created

gpart add -a 4K -s 800K -t efi ada0
ada0p1 added

gpart add -a 4K -s 4G -t freebsd-swap ada0
ada0p2 added

gpart add -a 4K -t freebsd-zfs ada0
ada0p3 added

gpart show -p ada0
=>      34  41942973    ada0  GPT  (20G)
        34         6          - free -  (3.0K)
        40      1600  ada0p1  efi  (800K)
      1640   8388608  ada0p2  freebsd-swap  (4.0G)
   8390248  33552752  ada0p3  freebsd-zfs  (16G)
  41943000         7          - free -  (3.5K)

gpart bootcode -b /boot/pmbr -p /boot/boot1.efifat -i 1 ada0
gpart: /boot/boot1.efifat: file too big (524288 limit)

gpart bootcode -b /boot/pmbr ada0
bootcode written to ada0

gpart bootcode -p /boot/boot1.efifat -i 1 ada0
<no output>

System is bootable.

-- 
+-------------------------------+------------------------------------+
| Vennlig hilsen,               | Best regards,                      |
| Trond Endrestøl,              | Trond Endrestøl,                   |
| IT-ansvarlig,                 | System administrator,              |
| Fagskolen Innlandet,          | Gjøvik Technical College, Norway,  |
| tlf. mob.   952 62 567,       | Cellular...: +47 952 62 567,       |
| sentralbord 61 14 54 00.      | Switchboard: +47 61 14 54 00.      |
+-------------------------------+------------------------------------+