There is an error in the configure script when using
--with-pgport= that will cause the compiled version of
PostgreSQL to no longer allow connections to the
new port and to treat shared memory improperly.

What happens is that if the port is changed, the configure
script defines DEF_PGPORT as "", which atoi() will return
as 0, which makes the IPC_KEY value 0. This then causes
semaphores to be allocated, but never released. Postgres
eventually returns from semget() with
"no space left on device". The source of this error could
easily be overlooked in version 6.3 since it is possible
to connect via UNIX domain sockets, and having DEF_PGPORT
defined as "0" would not be noticed until TCP was used.