Yes I'm sure about bpftp, like I said earlier the version is that 2.2.1.
I just got the results from ProFTPD 1.2.8, flashfxp says:
size xxxxx.img
213 4311377920
..and from linux itself the size is identical:
4.0gb (4,311,377,920)
So that can't be the source of resume probs, both seem to handle the size cmd.