data validation not working while we paste the values (for removing duplicates in a column

I suppose you could then recheck the validation with a macro after pasting.

Sub Checkval()
'
Dim testcell As String
Dim lr As Integer
lr = Cells(Rows.Count, "D").End(xlUp).Row
'just do the used rows in D

For i = 1 To lr

testcell = ActiveSheet.Cells(i, 4).Address

CheckValidation = Range(testcell).Validation.Value

If CheckValidation = False Then

MsgBox "fix validation in " & testcell
'or clear the cell or do something

Else
End If
Next i
End Sub