AndroidFastboot: discrepancy between relative and absolute paths

Initial situation

I got 2 systems: client and exporter, client has labgrid-client running and exporter, labgrid-exporter. I am in directory /build, which on client is a symlink to local file system /mnt/something, which is also exported via NFS. On exporter, /build is a symlink to that NFS share.

Steps to reproduce

Fastboot upload with absolute path works as expected:

$ labgrid-client -d -v fastboot flash rootfs $PWD/rootfs.img

DEBUG: Sending command: ['ssh', '-x', '-o', 'LogLevel=ERROR', '-o', 'PasswordAuthentication=no', '-o', 'ControlMaster=no', '-o', 'ControlPath=/tmp/labgrid-connection-xxxxx/control-exporter', 'exporter', "stat --format 'inode=%i,size=%s,birth=%W,modified=%Y' /build/rootfs.img"]

ManagedFile applies its heuristic and detects that both files are the same, so it foregoes a rsync from client to exporter.

While using a relative path doesn't:

$ labgrid-client fastboot flash rootfs ./rootfs.img

DEBUG: Sending command: ['ssh', '-x', '-o', 'LogLevel=ERROR', '-o', 'PasswordAuthentication=no', '-o', 'ControlMaster=no', '-o', 'ControlPath=/tmp/labgrid-connection-xxxxx/control-exporter', 'exporter', "stat --format 'inode=%i,size=%s,birth=%W,modified=%Y' /mnt/something/rootfs.img"]
DEBUG: remote: stat: unsuccessful error code 1

Here labgrid does a rsync between the systems.

Expected Behavior

Whether a relative or absolute path is used shouldn't change the behavior if both refer to the same file. They both should result in stat suceeding and no rsync.

I assume there's an erroneous path canonization somewhere.

Start in the AndroidFastboot and ManagedFile path-handling entry points, then reproduce the absolute and relative fastboot flash commands from the issue. Compare the paths used for remote stat; done means both forms identify the same file and avoid an unnecessary rsync.