You were just presented by Duplicate values conditional formatting type without further explanation. You were not warned, that you need a special formulas to discover real duplicates. and the results of showing duplicate values can be quite unexpected as you can see in the question or here:Д«ased on the above, I would say this is not a defect, but an unexpected and undocumented behavior.ДЄnd this poses a problem in real-life scenarios. It is possible that Excel simply uses its standard search algorithm (which honors wildcard characters) also for searching of cells with duplicate values. Д«ut back to duplicates: it can be discussed whether sample values PT_INTERNAL2859736 and *736 are duplicates by definition. functions like SEARCH(), SEARCHB(), COUNTIF().

On the contrary, support of wildcards is explicitly named in functionalities, where presence of wildcards is obvious and expected: Nowhere in these articles is mentioned that the internal algorithm searching for duplicates still respects wildcard characters ( *, ?, ~).

Highlight patterns and trends with conditional formatting.

Filter for unique values or remove duplicate values.

Microsoft documents the Duplicate Values mode of conditional formatting in the following articles:

The question unanswered before is if they are expected also in conditional formatting. Other answers reminded us of use of wildcard characters ( *, ?, ~) in Excel formulas. The way around it, is to use a formula to insert a tilde ( ~) in order to escape the asterisk ( *) for your conditional formatting: =COUNTIF(A:A,SUBSTITUTE(A1,'*','~*'))>1ДЄfter further research of the behavior and documentation, I can answer the question from high-level perspective: This is rather an undocumented behavior than a defect. It is indeed because * is treated as a wildcard.

Excel conditional formatting definition