Oracle Instant Client provides its own LDAP library that may be incompatible to the LDAP library provided by the operating system.
Segmentation faults and other errors can happen if you load an OCI8 extension into a PHP containing LDAP support or if you load a PHP module with OCI8 into an Apache server with LDAP support.
But this depends heavily on the exact versions of operating system, system LDAP library, PHP, OCI8, and other pieces of software involved.