I am using the following query to make an upsert:

MERGE INTO my_target_table AS target
USING (SELECT MAX(__my_timestamp) AS checkpoint FROM my_source_table) AS source
  ON target.name = 'some_name'
  AND target.address = 'some_address'
WHEN MATCHED AND source.checkpoint IS NOT NULL THEN
  UPDATE SET checkpoint = source.checkpoint
WHEN NOT MATCHED THEN
  INSERT (name, address, checkpoint)
  VALUES ('some_name', 'some_address', source.checkpoint)

Whenever it does 'insert', it also deletes from *my_source_table*. Any explanation why it deletes from *my_source_table* and can I avoid it, so the logic will stay the same, without anything being deleted from the source