Calculate method invoked with a smaller index than in previous invocation

Hi,

I noticed this behaviour when testing my indicator on a EURUSD 5tick chart. It's a recursive indicator which depends on previous calculated value, so the effect of this behaviour is that the previous value (which should be static after the bar is formed) is changed.

Here's some code to demostrate what I mean. It's not a big deal because I could easily circumvent this by checking if index < _lastIndex and then return without doing the calculation. But I'd like to highlight this anyways in case it's a bug.

int _lastIndex = -1;

public override void Calculate(int index)
{
    if(index < _lastIndex)
        Debug.WriteLine(index + " - incorrect?");
    else
        Debug.WriteLine(index);

    _lastIndex = index;
}

Best regards,
Vibra