A simple question about wrong sorting with multiple sort columns in Excel 2010

Hi, everyone! I have encountered a problem that I don't know how to explain.

So I post it here because I don't know if there is another more relevant forum...

I have a data sheet with the students' scores for the course. 

All the data were generated with the randbetween function,

and pasted with the values.

To rank the students by their performance,

I did the sort with the column "total score" as the first sort-column

and "final term" as the second.

The weird thing to me is that the order of the data seems problematic.

That is, all the rows are sorted correctly with the first sort-column.

But for the rows with the same values of the first sort-column,

there are some rows whose values of the second sort-column are out of order.

(please look at the data file at

Please change the "_dot_" to the real literal dot.

Especially the rows with 56.7 as the first sort-column value

and some other values near the tail of the list.)

I tried to manually input and sort the same values of both columns

in a near-by region. The result was correct.

When some friend copied all the data to paste in Notepad,

and reload them in excel. The problem disappears.

Some friend also tried to wrap a round function at the values of the 1st sort-column,

the sorting order became correct!

But they could not explain why either.

How confusing! I even tried to swap the first and secod sort-column;

the output was right.

All the data were generated by randbetween function and pasted with values.

Where could all the special characters, if any, come?

Can anyone give me an explanation? I would be very grateful.

Thanks in advance!