@kaznelson: Ah, so that's why the KeepAlive implementation was tweaked again ;p. Just as a random check: does it still happen with the latest development snapshot of PuTTy?
Anyway, I'll backport upstream's changes in the next builds, thanks for the heads up
. (In the meantime, you can switch SSHD to OpenSSH [EDIT: Or tweak SSH_DAEMON_OPTS in usbnet/lib/libkh[5] to remove the -K 15 switch]).