It's like saying:
Someone lends me 100 euros.
I give 1 euro to buy a chocolate (old times anyway)
I have 99 euros left.
I give back to the owner 1 euro, so I owe 99 more euros and have 98 euros in my hand.
99 euros i owe+98 euros i have=197 euros. Gratz, you just made 97 euros out of nothing by adding the money you have in your debt.
Same happened with this one, but your debt was 98 and the money you had 1, so 98+1=99 and you lost one euro.