This is only an issue when binding to an OpenLDAP server. There may be additional issues with LDAP on Lion server, but this problem as reported is an issue with Lion clients bound to servers running OpenLDAP without Kerberos or SSL.
Your use of the word "only" here is misplaced. This is a very serious security issue that affects clients connecting to OpenLDAP.
Indeed-for users that are bound to OpenLDAP its a massive issue. Without knowing those users exact setup its hard to know exactly what the issue is-the fact that its ONLY OpenLDAP servers is odd. The client must be receiving some sort of authentication succeeded message (you will note that it won't accept a blank password-so in that case OpenLDAP is responding with a failure). It may be a bug in Lion that triggers a bug in OpenLDAP.
It may also be possible for an attacker to impersonate an OpenLDAP server in order to induce (and exploit) the behavior.
which is possibly quite a few university macs in libraries and computer labs.
Really? Can you name even one university that uses LDAP but not Kerberos for their computer labs?
Well, I could name one that almost certainly doesn't, but I'll refrain.
In the Universities I've worked with, or visited, the computers in the labs (Macs anyway) have all been using Kerberos in one fashion or another-AD uses Kerberos, so does OpenDirectory (OS X directory offering).