Row numbers not updated after deleting entire rows

I am making an Excel macro to filter things, and therefore delete unnecessary rows. First I create a range of irrelevant cells (by making the union of them), and after that I delete the whole row for the given range.

deleteRng.EntireRow.Delete

So if I have a worksheet with 100 rows and the rows from 40 to 60 are irrelevant, that range is deleted and the rows from 60 to 100 shifted up, so totally I got 80 rows counted from 1 to 80. This works perfectly most of time, but with some special workbooks the row numbers not updated after the deletion, therefore in the previous example the rows counted like 1...40,61...100.

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Is there a workbook related setting which do this or what else could be the problem?