[BUG?] The first paste operation is different from the other paste

[tomitomy]

When I tested my Undo Redo function, I found this problem, it looks like a BUG, some people encountered such a problem?

Before using Cut or Copy, using the Paste operation will result in the lack of timely access to the pasted content:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls;
9.  
10. type
11.  
12.   TForm1 = class(TForm)
13.     bttnCopy: TButton;
14.     bttnPaste: TButton;
15.     bttnCut: TButton;
16.     Memo1: TMemo;
17.     procedure bttnCopyClick(Sender: TObject);
18.     procedure bttnCutClick(Sender: TObject);
19.     procedure bttnPasteClick(Sender: TObject);
20.     procedure FormCreate(Sender: TObject);
21.   private
22.   public
23.   end;
24.  
25. var
26.   Form1: TForm1;
27.  
28. implementation
29.  
30. {$R *.lfm}
31.    
32. procedure TForm1.FormCreate(Sender: TObject);
33. begin
34.   Memo1.Text := 'ABCD';
35. end;
36.  
37. procedure TForm1.bttnCopyClick(Sender: TObject);
38. begin
39.   Memo1.CopyToClipboard;
40. end;
41.  
42. procedure TForm1.bttnCutClick(Sender: TObject);
43. begin              
44.   writeln('Before Cut: ', Memo1.Text);
45.   Memo1.CutToClipboard;  
46.   writeln('After  Cut: ', Memo1.Text);
47. end;
48.  
49. procedure TForm1.bttnPasteClick(Sender: TObject);
50. begin
51.   writeln('Before Paste: ', Memo1.Text);
52.   Memo1.PasteFromClipboard;
53.   writeln('After  Paste: ', Memo1.Text);
54. end;
55.  
56. end.

I did the tests in Linux Mint 18.2 Mate, using Lazarus 1.8.0RC4 and 1.9.0(svn 56537M) GTK2

Is this a Bug?