In Backtests, Zorro seems to differentiate between compiling (and running the script) and just running the script. The latter just calls the run function and ignores everything else, which can cause problems when using global variables.
As an example:
// ---------------------------------------------------
int zaehler = 0;

function run()
{
StartDate = 20090520;
EndDate = 20120501;
zaehler++;

plot("asdf",zaehler,0,BLACK);

PlotWidth = 800;
PlotHeight1 = 320;
}
// -----------------------------------
With every subsequent run of this script zaehler is not reinitialised as 0 but keeps the value of the previous run, which is kind of strange for a Backtest.
My questions are:
1) How does this affect real trading?
and
2) Is there a way to code the example in a way it works properly on every run?

It is not only compiling and running - when you optimize and test a system, it can run through many cycles, dependin on your test method. You must initialize global and static variables at every cycle start.

The right way to do it is

if(is(INITRUN)) zaehler = 0;

Thank you, I will adapt my scripts.
I think it's still strange for a Backtest as I would expect the second run to lead to the same results as the first one.