AsyncProcess not firing OnReadData event

[dugga_doo]

I can't AsyncProcess1 to work correctly. As far as I can tell, OnReadData never fires.

I've tried stripping it right back to basics, like this.

Code: Pascal  [Select][+][-]

1.   TForm1 = class(TForm)
2.     AP1: TAsyncProcess;
3.     Button1: TButton;
4.     Memo1: TMemo;
5.     procedure AP1ReadData(Sender: TObject);
6.     procedure Button1Click(Sender: TObject);
7.   private
8.  
9.   public
10.  
11.   end;
12.  
13. var
14.   Form1: TForm1;
15.  
16. implementation
17.  
18. {$R *.lfm}
19.  
20. { TForm1 }
21.  
22. procedure TForm1.Button1Click(Sender: TObject);
23. begin
24.   AP1.Executable := '/usr/bin/cat';
25.   AP1.Parameters.Add('/etc/hosts');
26.   AP1.Options := [poUsePipes, poStderrToOutPut];
27.   AP1.Execute;
28.   while AP1.Running do
29.   begin
30.     memo1.Lines.add('Running');
31.     Sleep(200);
32.     Application.ProcessMessages;
33.     memo1.Lines.add('Done');
34.   end;
35. end;
36.  
37. procedure TForm1.AP1ReadData(Sender: TObject);
38. begin
39.   memo1.Lines.add('Read Data Here');
40. end;

The memo1 contents:

Code: Text  [Select][+][-]

1. Running
2. Done

As you can see, there are no 'Read Data here' lines, so the event is not firing.

Anyone got any ideas?
Am I missing a compiler option in my Lazarus or Project Options?
Is this some weird Linux/KDE/QT thing?

Operating System: Kubuntu 24.04
KDE Plasma Version: 5.27.12
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.13
Kernel Version: 6.8.0-136-generic (64-bit)
Graphics Platform: X11