Problems with Binary Replication

Hi,
I configured a master and a hot-standby server as described here:
http://wiki.postgresql.org/wiki/Binary_Replication_Tutorial#Starting_Replication_with_only_a_Quick_Master_Restart

At first everything looked ok.
Then some days later I find that at least some sequences on the
hot-standby are higher than those on the master.
I checked only one table with such a leaped sequence as primary key and
there where no entries for the higher sequence values.

How can this happen?