Version:           1.9.6 (enterprise 0.20070907.709405) (using KDE 3.5.8, Kubuntu (gutsy) 4:3.5.8-0ubuntu3.1)
Compiler:          Target: i486-linux-gnu
OS:                Linux (i686) release 2.6.22-14-386

I start to type a name in the "To:" field and kmail shows a drop-down list of names matching the letters I have typed.  The names are formatted as "Reverse Name with Comma" because that is how I have set them in address book.  If I now use the up and down keys to select the name I want, then each time I move the highlighter to a new name, the first bit of the previous name (up to and including the comma) gets left behind in the address field so that I end up with an address something like:

"Smith, "Smith, "Smith, "Smythe, John" <john.smythe@email.address>

Which is obviously invalid.