TIWGrid.cell[0,0] disappears in OnAsyncTimer

[MrSpock]

I can only one time assign
TIWGrid1.Cell[0,0].Control:= TIWImage1;
in form OnCreate

Another assignment to
TIWGrid1.Cell[0,0].Control
or even to any other cell
makes the cell [0,0] disappear

The bug is only in OnAsyncTimer
but it is all right (does not disappear) in OnTimer