Also seen with btrfs-progs:

08/07/2017 11:32:46 - DEBUG:Executing: gbp import-orig --no-merge --verbose --upstream-branch do-not-push --pristine-tar --no-interactive --no-symlink-orig '--upstream-tag=importer/upstream/ubuntu/%(version)s.xz' /tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz
gbp:debug: ['git', 'rev-parse', '--show-cdup']
gbp:debug: ['git', 'rev-parse', '--is-bare-repository']
gbp:debug: ['git', 'rev-parse', '--git-dir']
gbp:debug: ['git', 'for-each-ref', '--format=%(refname:short)', 'refs/heads/']
gbp:debug: ['git', 'show-ref', 'refs/heads/do-not-push']
gbp:debug: ['git', 'status', '--porcelain']
gbp:debug: ['git', 'rev-parse', '--quiet', '--verify', 'master:debian/changelog']
gbp:debug: ['git', 'tag', '-l', 'importer/upstream/ubuntu/4.12.xz']
gbp:debug: tar ['-C', '../tmpYwYgC4', '-a', '-xf', '/tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz'] []
gbp:debug: Unpacked '/tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz' to '../tmpYwYgC4/btrfs-progs-v4.12'
gbp:info: Importing '/tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz' to branch 'do-not-push'...
gbp:info: Source package is btrfs-progs
gbp:info: Upstream version is 4.12
gbp:debug: ['git', 'show-ref', 'refs/heads/do-not-push']
gbp:debug: ['git', 'rev-parse', '--quiet', '--verify', 'do-not-push']
gbp:debug: ['git', 'add', '-f', '.']
gbp:debug: ['git', 'write-tree']
gbp:debug: ['git', 'rev-parse', '--quiet', '--verify', 'do-not-push']
gbp:debug: ['git', 'commit-tree', 'ac65382da52adf93c3d699e05d457b48ccc9497a', '-p', '4e99aaf631ba2d755276eebdeae1812d1b108dc9']
gbp:debug: ['git', 'update-ref', '-m', 'gbp: New upstream version 4.12', 'refs/heads/do-not-push', '40abdd4c7d6ea40631f7888c07d27bdda5697ef0', '4e99aaf631ba2d755276eebdeae1812d1b108dc9']
gbp:debug: ['git', 'show-ref', 'refs/heads/pristine-tar']
gbp:debug: ['git', 'rev-parse', '--quiet', '--verify', 'pristine-tar']
gbp:debug: ['git', 'ls-tree', '-z', 'do-not-push', '--']
gbp:debug: ['git', 'mktree', '-z']
gbp:debug: /usr/bin/pristine-tar [] ['commit', '/tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz', 'ac65382da52adf93c3d699e05d457b48ccc9497a']
gbp:error: Import of /tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz failed: Couldn't commit to 'pristine-tar' with upstream 'ac65382da52adf93c3d699e05d457b48ccc9497a': pristine-xz failed to reproduce build of /tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz
(Please file a bug report.)
pristine-tar: command failed: pristine-xz --no-verbose --no-debug --no-keep gendelta /tmp/tmpirn2c01m/.git/git-ubuntu-cache/btrfs-progs_4.12.orig.tar.xz /tmp/pristine-tar.5dIvJGzDkH/wrapper
pristine-tar: failed to generate delta
gbp:error: Error detected, Will roll back changes.
gbp:info: Rolling back branch do-not-push by resetting it to 4e99aaf631ba2d755276eebdeae1812d1b108dc9
gbp:debug: ['git', 'update-ref', '-m', 'gbp import-orig: failure rollback of do-not-push', 'refs/heads/do-not-push', '4e99aaf631ba2d755276eebdeae1812d1b108dc9']
gbp:info: Rolling back branch pristine-tar by resetting it to 0eec71ef109cbfdaa7269280da0b5378f140035a
gbp:debug: ['git', 'update-ref', '-m', 'gbp import-orig: failure rollback of pristine-tar', 'refs/heads/pristine-tar', '0eec71ef109cbfdaa7269280da0b5378f140035a']
gbp:error: Rolled back changes after import error.
gbp:debug: rm ['-rf', '../tmpYwYgC4'] []