I am using dropdown combo (not dropdown list) on grid column.

On refresh method of combo I have:
This.DisplayValue = viewname.field1

On valid method of combo I have:
REPLACE viewname.field1 WITH This.DisplayValue IN viewname

Combo properties are:
rowsource is array (one dimension, character field).
BoundColumn = 1
BoundTo = .f.
ControlSource = (nothing)

Grid Column properties are:
bound = .t.
ControlSource = viewname.field1
Sparce = .f.

Always I write a new option on combo and move the focus to next column of the grid, the content of combo that I just have typed is cleared. After saving and refresh, the content of combo is showed.

Why the content of combo is cleared? What am I doing wrong?