Bug#589938: I understand that you are about to release a new stable version
This bug is a significant problem and has not been fixed on my machine with my
last update last night.
I suspect the kmail developers have fixed it already as I have not seen any
more reports about it being a problem, but I reported it again last night to
the kmail folks to see if I can find out more about it.
Previously the partially composed emails were in
~/.kde/share/apps/kmail/autosave but they are not there now.