I have the same issue, it seems, but AFAIK the problem is on the export side:
While the OVA logical file size matches the size of the VM's disk, the actual storage
usage on the VDO compressed and deduplicated NFS I use as export target per 'du -h
*.ova' is a mere 28KB, while 'strings <vm-name>.ova' reports an XML
header and then nothing but zeros.
I sure hope it's easy to fix and not an "we don't support importing oVirt OVA
exports..."