Extra $100 after borrowing and shopping I took \$1000 from my friend James and \$500 from Bond.
While walking to the shops I lost \$1000 so now I only have \$500.
I did some shopping, spending \$300 so now I have \$200 left.
I gave \$100 back to James and \$100 back to Bond.
Now my liabilities are \$900 for James and \$400 for Bond, so my total liabilities are \$1300.  
Total liabilities + Shopping = \$1300 + \$300 = \$1600, but I only borrowed \$1500.
Where did the extra \$100 come from?

That $\$1300$ already includes the $\$300$, along with the $\$1000$ you lost--that was your net loss of money for the day--you don't need to add it again.
The $\$900$ and the $\$400$ you still owe is just another way of reaching the same number.
