Windows XP, 5.01.2600
Messenger: 7.0.0425
Messenger Plus!: 3.40.0110
When I ping someone who doesn't have Plus! installed, and after sending the Ping I close the window, when I re-open the window I answer my own ping...
As you see, Messenger 7 displays last conversation, which includes the ping. When opening the window, it's me who replies the ping.