scp and rsync do not work (ssh works)
Solution 1:
I suspect that the misbehaving server has some unusual stuff in ~/.bashrc, ~/.profile or other startup scripts. Every time I've seen similar behaviour there has been some autorunning software on .bashrc or something similar.
Solution 2:
It seems to have been a once in a blue moon bug with the ISP. Happy that it has not occurred ever since. :-)