https://bugs.openldap.org/show_bug.cgi?id=9210
--- Comment #2 from lukas.juhrich@agdsn.de lukas.juhrich@agdsn.de --- If you wish, I can try to reproduce this again. Unfortunately, this has been two months ago and I've only come around to the bugreporting now, so I will need to downgrade and set some things up again.
The basic observation still stands though, adding the errno fixes the symptom.