ldap fails with LDAP search error: Invalid DN Syntax

My LDAP requests fail due to invalid DN syntax. Which is the "5C" chars inserted in LDAP query shown below, between "Lastname, firstname" Any ideas how that may be solved?

https://downloads-packages.s3.amazonaws.com/ubuntu-14.04/gitlab_7.9.0-omnibus.2-1_amd64.deb is what i installed

more details are enclosed in debug.txt[debug.txt]

(https://gitlab.com/gitlab-org/gitlab-ce/uploads/78438408157e9c810952a2ba1853ac38/debug.txt)

LDAP: searchRequest baseObject: CN=Lastname\5C, Firstname,OU=some,DC=example,DC=org

resultCode: invalidDNSyntax (34)

EDIT: the user gets created in gitlab after first logon attempt (so initial connection to ldap works and pulls info like email etc.) seems like its only the authentication part, where this problem arises. authentication then fails with "Access denied for your LDAP account." and the logs display the " Invalid DN Syntax", which is proved by the wireshark output.