Set the column to Sparse = .F.

Because you want normal date mark for not empty,
add another your class textbox to the column

column
  txtNormal
  txtEmpty  <=== this have DateMark
set
column.DynamicCurrentcontrol="IIF(EMPTY(datefield),'txtEmpty','txtNormal')"

you can build a TxtDate and on Init(),
add the txtEmpty and set DynamicCurrentcontrol to the Column.

Fabio