samba - Sep 2007 - Problems with BDC-Samba starting with version 3.0.25

I'm running Samba on Solaris 10 Sparc for about one year now (version 3.0.22
and then updated to 3.0.24). It acts as a BDC.
Now, after updating to 3.0.25c some users cannot log in.
I'm getting this error:
  domain_client_validate: unable to validate password for user myuser in domain
MYDOMAIN to Domain controller MYPDC. Error was NT_STATUS_NO_SUCH_USER.

The difference between the users is, that one are working on a desktop computer
logging in to the domain on startup, the other ones are working on a notebook
not logging in to the domain initially. They use local username and password
matching the entries in the domain.

No problem so far with 3.0.24 - connecting the shares worked fine. Starting with
with 3.0.25 it fails.
If I connect the share manually using "net use X: \\mysamba\myshare"
and specifying "MYDOMAIN\myuser" and password, it works.

What has changed? What am I doing wrong?
If you need the config and/or build options, let me know.

Thanks for your help!
Thomas