postgresql hanging (blocking) with smp kernel

I have a problem with postgresql runnung on smp kernel.

setup:

master:
-------
- Pentium 4 (hyperthreading)
- 2 GB Memory
- os: fedora core 1
- kernel: 2.4.22-1.2188.nptlsmp
- postgresql: 7.4.3-1PGDG

slave 1:
--------
- Pentium 4 (hyperthreading)
- 2 GB Memory
- os: fedora core 1
- kernel: 2.4.22-1.2115.nptlsmp
- postgresql: 7.4.3-1PGDG

slave 2:
--------
- Double Xeon (with hyperthreading)
- 2 GB Memory
- os: fedora core 1
- kernel: 2.4.22-1.2199.nptlsmp
- postgresql: 7.4.3-1PGDG

the "replication" is made by hand. reading from slave 1 or slave 2
(balanced) and wrtiting to master, slave 1 and slave 2. Our site is a
high-traffic site (the biggest dating-site in switzerland:
www.swissflirt.ch) with > 1400 concurrent users and > 40'000 visits
per day.

master and slave 1 (with pentium 4) are working perfectly with
smp-kernel. slave 2 (with double xeon) has big problems. running p.e.
with kernel 2.4.22 (non smp) works also but of course only one CPU is
used. when I use the smp kernel, the connections (and queries) are
hanging (blocking) after some short time. Also when I shutdown the
application (using java and jdbc to connect to the databases) the
postgres-processes (on slave 2) keep existing while the processes on
master and slave 1 shutdown propertly.

I also tried with other kernel-releases (the one on the master
2.4.22-1.2188.nptlsmp and the one on the slave 1
2.4.22-1.2115.nptlsmp) but it doesnt help neither.

does anyone know what this could be?

thanks alot
marcel