"gpart add" falsely claiming "No space left on device"

[Perry Hutchison]

I copied the 10.3-RELEASE memstick.img to a 4GB flash drive, then used
"gpart recover" to resize the partition table to the media.  After that
"gpart show" reports:

# gpart show da2
=>      3  7811067  da2  GPT  (3.7G)
        3       32    1  freebsd-boot  (16K)
       35  1348832    2  freebsd-ufs  (659M)
  1348867     2048    3  freebsd-swap  (1.0M)
  1350915  6460155       - free -  (3.1G)

but "gpart add" refuses to add a second freebsd-ufs partition in that
supposedly-free space:

# gpart add -t freebsd-ufs -l pkgs -f x da2
gpart: index '4': No space left on device

# gpart add -t freebsd-ufs -l pkgs -f x -b 1350915 -s 6460155 da2
gpart: index '4': No space left on device

All of these partitions are unmounted.

What am I doing wrong?