PropertyChanged?.Invoke(...) call calling the setter again when stepping through a Set statement

Question

I have a simple base class that implements INotifyPropertyChanged. The code works. But when I was stepping through a Set statement, when the Set statement called SetProperty(), I noticed that the PropertyChanged?.Invoke(...) call was calling the setter again.

So the setter code in the subclass looks something like:

private string someProperty ;
public string SomeProperty { get => someProperty ;
set {
    // Do some tests on value to make sure it's valid
    SetProperty(ref someProperty, value);
    // Now do some other stuff once that is set
}

When I step through it the call stack shows:

• SomeProperty.Set( valuetype value); ????? Why again???? --- 5
• External Code --- 4
• OnPropertyChanged(string propertyName ) --- 3
• SetProperty(field, value) --- 2
• SomeProperty.Set( valuetype value) ---- Initial set execution

Code snippet:

public abstract class ViewModelBase : INotifyPropertyChanged
{        
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        Dev.Tools.Assert(propertyName != null, "propertyName can't be null.... ");
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    // This is used to support change tracking.  But 
    //   the problem happens even when TrackChangedFields is false.
    // The EqualityComparer prevents this from being recursive.
    public virtual bool SetProperty<T>(ref T field, T newValue, [CallerMemberName] string propertyName = null)
    {
        if (!EqualityComparer<T>.Default.Equals(field, newValue))
        {
            field = newValue;
            OnPropertyChanged(propertyName);

            if (TrackChangedFields && !IgnoreFieldList.Contains(propertyName))
            {
                ChangedFieldList.Add(new ChangedRecordDetail(propertyName, field, newValue, ViewModelName));
            }
            return true;
        }
        return false;
    }

Any idea why the PropertyChanged?.Invoke() call is causing the set to fire again?

Again, this code works fine. I just don't understand why the 2nd call to the setter is happening nor what to do to only have the setter called once.