I had the same setup working fine on a single-core machine.
The problem shows up especially when using the Subversive plugin for Eclipse. Running top you have one, sometimes more than one apache processes running at 100% utilization. Could it be a deadlock? Switching on verbose debugging in slapd seems to reduce, but not eliminate the problem.
The only way I have found to get rid of the problem is to stop apache, kill the remaining apache processes, then restart apache. This obviously isn't much good to us.