logtrigger/denyaccess triggers removed from master/slave

Hi All

I am using postgres-8.1.2 and slony-1.1.5 for replication.
I have 1 master and 1 slave in my cluster.
Sometimes I see problem of missing logtriggers and denyaccess triggers
on master table and slave tables respectively. Replication don't take place in that
state though systems are properly shown as master and slave.
This problem is resolved by dropping the schema used by slony on both the systems an
then recreating the schema.

I want to know what could be the root cause of logtriggers/denyaccess
triggers getting removed from the tables.

Thanks in advance

Regards
Tamanna