Bug in Build 646?? - re: Bars function and for loop - very very weird!

Hello MQL4 folks - I've been coding in MQL4 for a long time... this morning I was writing some code and noticed some very weird behaviour...... in the end I wrote a billy basic test routine and quite frankly I can't explain what on earth is going on here...  

Try this:- 

int OnInit()

  {
  Do_Calc();
  return(INIT_SUCCEEDED);
  }

int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])

  {
  return(rates_total);
  }

void Do_Calc()
{
int p;
int b=Bars;
Print ("Bars=",Bars);
Print ("Test");
for (p=0; p<b; p++)
      {
      Print (p);
      }
}        

Experts output:

Errr..... OK ...  so the print statement were skipped and the loop jumps straight to 297....  I can't explain this at all... doesn't seem logical.

If you change the max iteration value in the loop to an integer such as 100... the program runs OK - so code mod to:-

 void Do_Calc()
{
int p;
int b=Bars;
Print ("Bars=",Bars);
Print ("Test");
for (p=0; p<100; p++)
      {
      Print (p);
      }
}

experts op:

So it appears there's a bug to do with the Bars function.... has this been deprecated?? 

MQL4 Ref makes direct reference to Bars in for loop..... 

Doesn't seem to work so well in Build 646 - tried rebooting machine - purging memory - copying code to new indy... makes no sense at all!