[ubuntu] .dmrc written from openSuse not compatible with ubuntu ?

Hi there,
we have computer pools where about 1000 users can login. On a maschine is openSuse and Ubuntu installed. The users choose over the boot manager, which system to start. The home directory from each user is on a nfs-file-system. So does'nt matter, which OS the user starts, the home directory is the same in openSuse and ubuntu.

There is a strange problem with the .dmrc file. When a user was logged in in openSuse and then tries to login into ubuntu, the login does'nt work. There is no error message at all, it just behaves like the user entered the wrong password.
After the user deleted his .dmrc file, the login works again.
Only ubuntu has problems with the .dmrc file, when the user was logged in in openSuse before. openSuse has no problems, when the user was logged in in ubuntu.
We checked the content of the .dmrc file, the rights, we couldn't find something strange. It's also not easy to reproduce, there are a lot of users, where this problem does'nt happen. We compared everything between users, where the error happens and other users where it does'nt, we did not find a difference.

Anybody an idea ?

thanks in advance