The debug output shows that a read attempt was queued up for a socket that was closed. This is a normal occurrence when an LDAP client closes its connection immediately after sending its last request (Unbind here) and slapd doesn't have enough CPU resources to process the read attempt immediately.
Just because of not enough CPU? Are you sure?
This is a local test server on a 99% idle dual-core notebook which did not do anything else than processing a single search and after the client received all the results (72 entries, few short text attributes) the client sends the unbind. Nothing else is happening. And I can reproduce it everytime.
If you're reporting a hang with OpenLDAP, you should have said that explicitly. If not, then I see no bug here and this ITS will be closed.
I'm so cautious about this because I had a situation where a slapd process (a provider) died several times. And the last message seen in the syslog was exactly "connection_read(20): no connection!".