Hi Emmanuel,
Your patch needs an improvment. When I run the test new rows are added to the property_attribute_device table (which is wrong).
MySQL is clever enough to see if modification is done or not, i.e.
mysql_affected_rows(…) return 0 if row has not been changed (but update has been executed).
So it is better to check if the insert query should be executed in another way, e.g. by a select query.
Cheers,
Jan