Checkbox in a Column

Hello,

I have a Matrix-Column as a checkbox. Now i want do check/uncheck all Checkboxes in the Matrix with one button-click

   
oform.Freeze (True)
For i = 1 To 64
  oColumn.Cells(i).Specific.Checked = True
Next
oform.Update
oform.Freeze (False)

It works and all Checkboxes will be checked. But if i scroll down in my matrix the arrow in the box will be removed, but the checkbox is still checked. It seems that it is a Refresh-Problem?

Any ideas to solve this?

Thanks

Chris