Data Validation's Custom formula for some reason doesn't work for named range in Excel 2013. In example, I have a whole A column but the header, i.e. $A$2:$A$1048576, named as 'id'. The formula =COUNTIF(id,A2)=1 correctly gives TRUE or FALSE when used in other cell for test but it doesn't affect the data validation - it allows duplicate entries. However when used directly =COUNTIF($A$2:$A$1048576,A2)=1, it works for validation as well (not allowing duplicate entries in said column), giving exactly the same results in other cells as the version with named ranges.
//EDIT for clearance: $A$2:$A$1048576 is a named range named as 'id'.