Child controls of TCustomControl flicker when TGridPanel is in between - delphi

Question

I have following DFM structure:
inherited FormSwitches: TFormSwitches
DoubleBuffered = True
object PnlMain: TPanel [0]
object pnlControl: TPanel
DoubleBuffered = True
ParentDoubleBuffered = False
object GridPanel1: TGridPanel
ParentFont = False
object pnlWP21: TPanel
object btnInfoWP21: TSpeedButton
end
object lblWP21: TLabel
end
object btnWP21: TcxButton
end
end
object pnlBuffWP21: TPanel
object lblBuffWP21: TLabel
end
object btnBuffWP21: TcxButton
end
end
end
end
end
end
Each row of GridPanel is identical to the others, so I provide here only one of them.
Here is the more detailed variant of it:
inherited FormSwitches: TFormSwitches
DoubleBuffered = True
object PnlMain: TPanel [0]
Align = alClient
object pnlControl: TPanel
BevelOuter = bvNone
BorderWidth = 10
BorderStyle = bsSingle
DoubleBuffered = True
ParentDoubleBuffered = False
object GridPanel1: TGridPanel
Align = alClient
ColumnCollection = <
item
Value = 50.000000000000000000
end
item
Value = 50.000000000000000000
end>
ControlCollection = <
item
Column = 0
Control = pnlWP21
Row = 1
end
item
Column = 1
Control = pnlBuffWP31
Row = 3
end
item
Column = 0
Control = pnlWP22
Row = 2
end
item
Column = 1
Control = pnlBuffWP22
Row = 2
end
item
Column = 0
Control = pnlWP31
Row = 3
end
item
Column = 0
Control = pnlWP32
Row = 4
end
item
Column = 1
Control = pnlBuffWP32
Row = 4
end
item
Column = 0
Control = Panel9
Row = 0
end
item
Column = 1
Control = Panel10
Row = 0
end
item
Column = 1
Control = pnlBuffWP21
Row = 1
end>
ParentFont = False
RowCollection = <
item
Value = 20.598092313651590000
end
item
Value = 19.243163829564510000
end
item
Value = 19.512568123178410000
end
item
Value = 20.774380861810620000
end
item
Value = 19.871794871794870000
end>
object pnlWP21: TPanel
Align = alClient
Padding.Left = 3
Padding.Top = 3
Padding.Right = 3
Padding.Bottom = 3
object btnInfoWP21: TSpeedButton
AlignWithMargins = True
Margins.Left = 0
Margins.Top = 0
Margins.Bottom = 0
Align = alLeft
end
object lblWP21: TLabel
Width = 50
Align = alRight
Alignment = taCenter
AutoSize = False
Caption = '0'
Transparent = True
Layout = tlCenter
end
object btnWP21: TcxButton
Align = alClient
Caption = 'Workplace 2-1'
SpeedButtonOptions.GroupIndex = 1
end
end
object pnlBuffWP21: TPanel
Align = alClient
Padding.Left = 3
Padding.Top = 3
Padding.Right = 3
Padding.Bottom = 3
object lblBuffWP21: TLabel
Width = 50
Align = alRight
Alignment = taCenter
AutoSize = False
Caption = '0'
Transparent = True
Layout = tlCenter
end
object btnBuffWP21: TcxButton
Align = alClient
Caption = 'WP 2-1 BUFF'
SpeedButtonOptions.GroupIndex = 1
end
end
end
end
end
end
In this form I create an instance of TCustomControl:
TFormSwitches = class(TStdFrmNoneDB)
private
FLayout: TWPDrawing;
public
constructor Create(AOwner: TComponent); override;
end;
constructor TPrjFormPTLBufferingSwitch.Create(AOwner: TComponent);
begin
inherited;
FLayout := TWPDrawing.Create(Self);
FLayout.Parent := Self;
FLayout.Align := alClient;
FLayout.OnResize := WPLayoutResizeHandler;
pnlControl.Parent := FLayout;
end;
Its class sets the csAcceptsControls flag so that child controls of FLayout aren't flickering as the drawing is repainted.
TWPDrawing = class(TCustomControl)
public
constructor Create(AOwner: TComponent); override;
end;
constructor TWPDrawing.Create(AOwner: TComponent);
begin
inherited;
DoubleBuffered := True;
ControlStyle := ControlStyle + [csAcceptsControls];
end;
and they aren't flickering if they are simple TButtons having FLayout as their direct parent.
Everything changes when I drop the controls onto TGridPanel. They start flickering intensively (although not so wild as without the csAcceptsControls flag).
Each has DoubleBuffered = True. What else could be done to prevent flickering?