Control.InvokeRequired changing throughout a method

Question

Look at these screenshots. First shows a breakpoint in my code and shows current value of InvokeRequired.

Seconds screenshot shows value of InvokeRequired after pressing F10 (step over) one time in debugger (IF statement content is not entered, ELSE is).

What happens next, is InvalidOperationException on rtbOutput, because I try to change its fields in ReportProgress. Here is how I call OnProgressReported:

public event EventHandler<BuildProgressEventArgs> BuildProgresReported = delegate { };

public void InvokeReportBuildProgress(BuildProgress progress)
{
    BuildProgresReported.Invoke(this, new BuildProgressEventArgs(progress));
}

How is this even possible? Is there other, better way to detect if Invoke should be called?

Update:

I have changed method code to the following:

public void OnProgressReported( object caller, BuildProgressEventArgs progressEventArgs )
        {
            if( rtbOutput.InvokeRequired )
            {
                Debug.WriteLine($"Invoke was required on thread: #{Thread.CurrentThread.ManagedThreadId} named '{Thread.CurrentThread.Name}'");
                rtbOutput.BeginInvoke( new Action( () => OnProgressReported(caller, progressEventArgs) ) );
            }
            else
            {
                Debug.WriteLine($"Invoke was NOT required on thread: #{Thread.CurrentThread.ManagedThreadId} named '{Thread.CurrentThread.Name}'");
                if ( this.IsDisposed )
                {
                    throw new InvalidOperationException( "This form has been disposed" );
                }

                rtbOutput.Text = "abc";
                rtbOutput.Text = "xxx";
                //ReportProgress(progressEventArgs.Progress);
            }
        }

The only output is

Invoke was NOT required on thread: #15 named ''

and the method this throw an exception on line rtbOutput.Text = "abc";

HOWEVER! When the line rtbOutput.Text = "xxx"; is commented out, everything works fine, even though rtbOutput.Text = "abc"; is still present!

Update #2 - solution:

The problem was a window handle that was not yet created (I subscribe to an event right AFTER creating the window) I have to wait for handle to be created using

this.IsHandleCreated