FileAppend - generates many duplicate entries -???

[Ian MacAuslan <imacauslan@xxxxxxxxxx>]

I've written a simple piece of code to just copy out to a disk file the 
P&L of a trade whenever a trade is closed out.  It appears there is a 
bug somewhere--or perhaps I'm not doing something quite right.  Executed 
on the bar immediately following a position being closed out, It should 
write out simply the symbolname and the P&L of that last 
trade...Instead, I get many duplicate lines, though not apparently any 
particular number of duplicates.  

Here is the code, which I paste into the bottom my strategy--any 
strategy, take one of the canned ones from TradeStation:
=====
vars: MP(0), plstring("");

MP = MarketPosition;

if MP = 0 and MP[1] <> 0 then begin
    plstring = GetSymbolName + ", " + PositonProfit(1) + NewLine;
    FileAppend("c:\mytrades.txt", plstring);
end;
=====

Here is what I tend to get in the output file:

IBM, -280.00
IBM, -280.00
IBM, -280.00
IBM, -280.00
IBM, -280.00
IBM, -280.00
IBM, -280.00
IBM, -224.00
IBM, -224.00
IBM, -224.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00
IBM, 880.00

Anyone else had this problem?  Am I doing something wrong?

THANKS!