There is a bug in the demo. In "Tfmain.btnAddTextClick" method insert this code:
ImageEnVect1.ObjMemoCharsBrushStyle[-1] := bsClear;
It must be inserted in:
.....
if btnAddText.Down then
begin
ImageEnVect1.MouseInteractVt:=[miPutMemo];
ImageEnVect1.ObjFontLocked[-1]:=false;
ImageEnVect1.ObjMemoBorderStyle[-1]:=psClear;
ImageEnVect1.ObjMemoCharsBrushStyle[-1] := bsClear; // <<<< INSERT THIS
tmpFont:=TFont.Create;
tmpFont.Color:=clRed;
tmpFont.Size:=14;
tmpFont.Name:='Arial';
.....