delphi form constraint doesn't work when maximized - delphi

Question

i try to maximize width and hold height. i use delphi xe4, windows 7, 1,440 * 900 2 monitors.
height constraint usually works well but when it exceeds certain value which is 859 it doesn't work.
i guessed that it was because of windows snap feature but even after the turning off that it's same.
when i do this in the sub monitor which doesn't have taskbar and in the main monitor with taskbar auto hide it works well. it seems the trouble with taskbar.
any help to solve this please. thanks.
procedure TForm1.Button1Click(Sender: TObject);
begin
Constraints.MaxHeight := 859; // works well
WindowState := wsMaximized;
Caption := IntToStr(Height);
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
Constraints.MaxHeight := 860; // doesn't work
WindowState := wsMaximized;
Caption := IntToStr(Height); // maximized as 876
end;
procedure TForm1.FormConstrainedResize(Sender: TObject; var MinWidth, MinHeight, MaxWidth, MaxHeight: Integer);
begin
MaxHeight := 860; // doesn't works and is maximized as 876
end;

Answer 1

If you are trying to restrict the maximum size of the form when the user tries to maximise it then this will work. I have my own Form class descended from TForm called TRGNewForm and all my forms descend from that. However the scheme will work for the form you put the code in.
In the Interface section, in your Form class Public definition
{ Trap Sys Commands }
procedure WMSysCommand (var Msg: TWMSysCommand); message WM_SYSCOMMAND;
In the Implementation
procedure TRGNewForm.WMSysCommand (var Msg : TWMSysCommand);
begin
{ If MdiChild and Maximize button pressed, then use our own routine,
as Windows has a bug }
if (Msg.CmdType = SC_MAXIMIZE) and
(FormStyle = fsMDIChild)
then Maximise_Child_Form
else DefaultHandler (Msg);
end;
In Maximise_Child_Form you set the height and width as required.