Some clarification on your calculation.
one to the person his sending 0.85 BTC to while the other to himself as change of 0.15 BTC (the remaining digit wey go Dey show for the balance after the transaction).
You didn't account for fee
So the change (UTXO of Mr A) should be lower.
The case of UTXO came to my head when I heard about some wallet branding some coins as tainted.
They don't brand the wallet address but the UTXO of the received tainted coin.
Say Mr A has 0.1 Btc and received 0.05Btc that is considered tainted
As long as he spent only from the 0.1BTC is transactions remains clean (can be selected manually via coin control, electrum does it)
But if it collects any from 0.05btc no matter how small
It becomes tainted since the new UTXO now has a relationship with the
clean one.