Why the code to create copy of portfolio equity produce different backtest result?

Hi,
I am using the code to create copy of portfolio equity as suggested here.
http://www.amibroker.com/kb/2006/03/11/how-to-create-copy-of-portfolio-equity/

As my test...
With some systems, when I switch between activate and deactivate(using comment out) this part of code,
the backtest result keep being exactly the same.

But with some other systems, when activate/deactivate this part of code,
the backtest result is different. (as my test...it is a lot different)

FYI, I also read this guideline but don't understand cleary
www.amibroker.com/kb/2014/05/07/why-do-backtest-results-change/

So...is this (the difference of backtest result) the possible scenario when we use the code?
Is there anyway we can make it producing the same backtest result all the time?
And should we concern to make it producting the same backtest result all the time?
Is this related to "flags" option in Addtocomposite function?
(I use both atcFlagDeleteValues | atcFlagEnableInPortfolio as suggested in that above URL.)

Could anyone understand and explain me about this?

Thank you,
Patchawat K.