Thank you for taking the time to report this issue and help to improve Ubuntu.
From what I can see, this is a duplicate of bug #314222, which was fixed in Ubuntu 9.04. Marking as such.
Since Ubuntu 8.10 reaches end-of-life in three months, my recommendation is that you upgrade to Ubuntu 9.04 or Ubuntu 9.10 if the behavior of pam_limits in 8.10 is a problem for you.
Thank you for taking the time to report this issue and help to improve Ubuntu.
From what I can see, this is a duplicate of bug #314222, which was fixed in Ubuntu 9.04. Marking as such.
Since Ubuntu 8.10 reaches end-of-life in three months, my recommendation is that you upgrade to Ubuntu 9.04 or Ubuntu 9.10 if the behavior of pam_limits in 8.10 is a problem for you.