Conditional Formatting (highlighting duplicates) oddity in Excel

Hello,

I've noticed something in Excel (2007) which seems very odd when using:

    Home tab > Conditional Formatting > Highlight Cells Rules > Duplicate Values >

and certain characters are present.  I'm first interested in knowing if the same thing happens in all installations of Excel or just mine -- and if it does, I'm very curious to know why.

Trying to adequately explain what happens (even with an uploaded file or screenshots) would, I'm afraid, be problematic but you can create the same thing in only a minute or two:

Open a blank spreadsheet and in some single column, enter the following values in any four cells:

    1st cell:            >3d
    2nd cell:      >3d
    3rd cell:            a
    4th cell:            b

Now select that entire column and go to

    Home tab > Conditional Formatting > Highlight Cells Rules > Duplicate Values >

      1st drop down menu > Duplicate
      2nd drop down menu > Light Red Fill with... (any choice is OK)

In my Excel, the two cells with ">3d" are highlighted as expected but each of the following maneuvers and its result seems very odd to me:

    1)  If I delete either of the highlighted entries, the remaining cell is still highlighted -- even though it no longer has a duplicate. (Thus the test has produced a false positive.)

    2)  If both ">3d" entries are present and I delete either "a" or the "b" the shading goes away, (a false negative).

    3)  If I remove any of the three characters in ">3d" (i.e. ">" or "3" or "d"), the highlighting goes away for that entry.

    4)  I can replace the ">" with "<" and get the same result.

    5)  I can replace "3" with any number and/or "d" with any text and get the same result.

    6)  If I go back to:      Home tab > Conditional Formatting > Highlight Cells Rules > Duplicate Values > 1st drop down menu > and select "Unique" in place of "Duplicate," the unexpected or odd behavior persists.

    7)  If I go to Data tab > Remove Duplicates, it eliminates one of the duplicates as it should.

Again, I'm curious to know if Excel does this for all users and if so, why.

Thanks