The value you see loginEmail:: IGpvY2tleTc1QGhvdG1haWwuY29t is $ echo -n 'IGpvY2tleTc1QGhvdG1haWwuY29t' | base64 -d && echo "" email@example.com (note the leading space). I suspect garbage in-garbage out, where LDAP browser is probably hiding garbage by trimming the leading space. You should check with ldapsearch(1) instead. Looks like incorrect data rather than a bug in slapcat(8). p.