Randomly missing contact lists

Has anyone experienced users of the Spark client sometimes seeing contact lists and sometimes not?

We have a few users that once in a while do not see the contact list.

The contact list is a shared group; the group being an LDAP group that all the members belong to.

We are using:

Openfire Enterprise

3.4.4; we were seeing this problem before the 3.4.4 upgrade as well.

Thanks!