[Hampshire] badblocks -w error?

I have been running a badblocks test on a partition on one of the desktops.

I am puzzled by the output and would be grateful for an interpretation.
Googling has got me nowhere. Perhaps I am asking the wrong questions
again :-(

root!tty1:/# badblocks -w /dev/hdb6
^[[24~root!tty1:/# 4~

This is as accurate a copy as I can produce. The spaces, or lack of them, are
all in the right places. But the tilde is not. It is actually at the top of
both 4s, where this star is: 4*

TIA
Lisi