What about this one:
A buys 1000, transfers to B (A: 0, B: 2000).
B transfers 2000 back to A (A: 4000, B:0).
A transfers 4000 back to B (A: 0, B:8000).
B transfers 8000 back to A (A: 16000, B:0).
A transfers 10000 back to B (A: 6000, B: 20000).
B transfers 20000 back to A (A: 46000, B: 0).
A transfers 10000 back to B (A: 36000, B: 20000).
B transfers 20000 back to A (A: 76000, B: 0).