Version:            (using KDE 4.2.0)
OS:                Linux
Installed from:    Unlisted Binary Package

Hi,

I'm using the Debian experimental packages.

Steps:
1) Log in to a remote machine (ssh -CX example.org) (might need to be via a limited-bandwidth connection; 5 Mb/s in my case).
2) Start kmail.
3) Create a new message.
4) Start typing. You'll see each letter added at about 1 per second.
5) For comparison, start kwrite or kate and start typing. You'll see bunches of letters added with lag, but they tend to keep up.

It seems there's an awful lot of X traffic for each letter, one after the other, using the kmail composer.

Peace,
Brendon