Autofill changes formulas strangely

[nfshp253]

I have this formula at cell E2:

=RIGHT($D2&"-"&COUNTIF($D$2:$D2,$D2),LEN($D2&"-"&COUNTIF($D$2:$D2,$D2))-FIND("-",$D2&"-"&COUNTIF($D$2:$D2,$D2),FIND("-",$D2&"-"&COUNTIF($D$2:$D2,$D2))+1))

This is to find the instance/occurrence of the value at D2 counting from above, but not below it.

Logically to me, when Excel autofills, the formula at E3 shoud be:

[QUOTE}=RIGHT($D2&"-"&COUNTIF($D$2:$D3,$D3),LEN($D2&"-"&COUNTIF($D$2:$D3,$D3))-FIND("-",$D3&"-"&COUNTIF($D$2:$D3,$D3),FIND("-",$D2&"-"&COUNTIF($D$2:$D3,$D3))+1))[/QUOTE]

But instead, when autofilling, the first formula changes to this:

=RIGHT($D2&"-"&COUNTIF($D$2:$D8,$D2),LEN($D2&"-"&COUNTIF($D$2:$D8,$D2))-FIND("-",$D2&"-"&COUNTIF($D$2:$D8,$D2),FIND("-",$D2&"-"&COUNTIF($D$2:$D8,$D2))+1))

The fourth formula becomes this:

=RIGHT($D5&"-"&COUNTIF($D$2:$D8,$D5),LEN($D5&"-"&COUNTIF($D$2:$D8,$D5))-FIND("-",$D5&"-"&COUNTIF($D$2:$D8,$D5),FIND("-",$D5&"-"&COUNTIF($D$2:$D8,$D5))+1))

And even worse, the fifth formula becomes this:

=RIGHT($D6&"-"&COUNTIF($D$2:$D11,$D6),LEN($D6&"-"&COUNTIF($D$2:$D11,$D6))-FIND("-",$D6&"-"&COUNTIF($D$2:$D11,$D6),FIND("-",$D6&"-"&COUNTIF($D$2:$D11,$D6))+1))

Why is this happening? Why is the array not expanding step-by-step? And why would the first formula change on its own? The data comes with headers and are formatted as a table.