The Stats Aggregation Service normally runs in its own separate JVM but for a 64-bit JVM that is not necessary. The separate JVM feature was disabled as follows and that resolved the problem:
a. Stop the Enterprise Manager (EM)
b. Edit the file EM_HOME/config/tess-default.properties
c. Change the property"dailystats.aggregateInSeparateJvm=true" to be false i.e. "dailystats.aggregateInSeparateJvm=false"
NOTE: Before restarting the EM the excessive ts_st_ts_all_dly_<date> table partitions already created also need to be deleted from the cemdb
For the case that highlighted this problem it was a new install so the cemdb was dropped and new database/schema created with the EM installer.
d. Start the EM