ubuntu-device-flash fails for beagleblack with "more partitions then expected while creating loop mapping"

[Winston Smith]

Trying to build a custom images for the Beaglebone Black using the "Snappy for Devices porting guide". However, ubuntu-device-flash fails as follows:

$ sudo ubuntu-device-flash core 15.04 -o my-snappy.img --size 4 --channel stable --oem beagleblack --enable-ssh --device-part=./device.tar.xz
Determining oem configuration
Starting download of beagleblack
280.74 KB / 280.74 KB [==================================] 100.00 % 433.44 KB/s
Done
Fetching information from server...
Downloading and setting up...
issue while mapping partitions: more partitions then expected while creating loop mapping

Host system is Ubuntu 14.04 x64, all software up to date. I did try purging the cache.