Alphanumeric sorting

This is a guess.

I don't think Excel can read 49816-1631 as a number. That is to say, it's NOT a number, not until you (or Excel) does the subtraction. In the meantime, it is, by definition, text. Now, maybe it's a zip code (the way it's formatted, that occurs to me as a possibility). Are those other columns you refer to, where you get prompted to sort as numbers, also "numbers" mixed with text in the same field? If they really are just arabic numerals, even if formatted as text, then Excel is smart enough to treat as numbers, but what you have here, with the "-" dividing one set of numerals from another is text and can't be other than that. 

As I said, it's a guess, but a semi-informed one. If you'd care to post the spreadsheet, or a portion of it, we can test my hypothesis.