I don't know wheather this bug is upstream related or Debian only, but Squeeze
is frozen so I better report it here (in Debian BTS).

1. Press "Compose Message"
2. Press "To:"
3. Select LDAP Adressbook

Problem:
A new "Enter password" window appears, cursor is blinking in the selected
window (no password stored in keyring) so it seems to be fine
BUT:
The Password "MySecretPassword" appears in the background window with title
"Select Contacts from Adress Book" under "Search:"

I made a screenshot (80kb):
http://www.chbmeyer.de/evolution.png

There is no way to enter the password in the right field - there is only a
workaround: Press "Esc", then the "Select Contacts ..." window closes,
you now can enter the LDAP-password and then try to adress your Mail.

Christian Meyer