Why did it propose a harvest and a negative for the same term?

A proven query can earn an exact keyword for its own product. An exact owned by a different proven product does not prevent that product independently qualifying from its own source ad group's clicks and orders. Same-product duplicates and unknown ownership remain protected.

A harvest may include a paired Source block when a separate source lane should stop matching the query. The block waits for proof the new exact is serving in a later check. If it never serves, the block expires.

Never put the negative in the destination ad group: it would suppress matching traffic for every positive there, including the exact you wanted to keep. When source and destination are the same ad group, withhold the source block. Read the proposal's actual legs and scope; a duplicate alone does not prove higher auction prices or authorize a negative.