SpecialCells(xlCellTypeConstants) results unexpected result on just one cell as the base range

Question

To summarize: if the base range of the SpecialCells is just one cell, then the result of range.SpecialCells(xlCellTypeConstants, xlNumbers) yields not just that cell or nothing. I supposed, SpecialCells should yield a range inside that object it is applied... or am I wrong?

I've "developed" a little new excel book, just to show what I don't understand, as follows:

1. Created a new excel book

2. Filled the A1:B3, as follows:

      A   B   ...
    1 1  12
    2 2  22
    3 3  32
    .
   

   All the other cells of the sheet are untouched.

3. Inside a new module I've added the following code:

   Private Sub test()
   
       Dim oSet As Range, oSpec As Range, oUsed As Range
   
       Worksheets("Sheet1").Activate
   
       Set oSet = ActiveSheet.Range("A1:A1")
       Set oSpec = oSet.SpecialCells(xlCellTypeConstants, xlNumbers)
       Set oUsed = ActiveSheet.UsedRange
   
       Set oSet = Nothing
       Set oSpec = Nothing
       Set oUsed = Nothing
   
   End Sub
   

4. Running the subroutine, and stopping it at the first range reset, it yields:

   oSet.Address = "$A$1"
   oSpec.Address = "$A$1:$B$3" ' this seems to be wrong; should it be just "$A$1" ?
   oUsed.Address = "$A$1:$B$3"
   

5. Having been changed the value of A1 to A, rerun the sub, and stop at the same place, it gives (consistently with the previous, which shows it works consequtively):

   oSet.Address = "$A$1"
   oSpec.Address = "$B$1","$A$2:$B$3" ' this seems to be wrong; should oSpec be nothing ?
   oUsed.Address = "$A$1:$B$3"
   

6. However, resetting the value of A1 to the original 1, but changing the range of the first Set operation in the Subroutine from just the cell "A1" to a true range of cells "A1:A2", then rerun the sub, and stop at the place, it gives very different (and more expected) result:

   oSet.Address = "$A$1:$A$2"
   oSpec.Address = "$A$1:$A$2" ' this is good
   oUsed.Address = "$A$1:$B$3"
   

I would appreciate, if somebody would explain the results. Thanks ahead.

Answer 1

This is happening because in case of one cell, it considers UsedRange instead.
References:
1) Super secret SpecialCells
2) Using SpecialCells in Excel VBA

As a helpful note, I will give you my wrapper function for SpecialCells and its helper method (in C#, not in VBA):

    /// <summary>
    /// <para>Wrapper for SpecialCells function.</para>
    /// </summary>
    /// <param name="inputRange"></param>
    /// <param name="cellType"></param>
    /// <returns></returns>
    /// <remarks>Throws null when there are no cells in <paramref name="inputRange"/> corresponding to <paramref name="cellType"/>, unlike SpecialCells which throws exception</remarks>
    public static Range GetRangeSpecialCells(this Microsoft.Office.Interop.Excel.Range inputRange, XlCellType cellType)
    {
        try
        {
            if (inputRange.Cells.Count == 1)
            {
                if (cellType == XlCellType.xlCellTypeComments)
                {
                    if (inputRange.Comment != null)
                    {
                        return inputRange;
                    }
                    else
                    {
                        return null;
                    }
                }
                else if (cellType == XlCellType.xlCellTypeFormulas)
                {
                    if (inputRange.HasFormula == true)
                    {
                        return inputRange;
                    }
                    else
                    {
                        return null;
                    }
                }
                else if (cellType == XlCellType.xlCellTypeBlanks)
                {
                    if (string.IsNullOrEmpty(inputRange.Value2) == true)
                    {
                        return inputRange;
                    }
                    else
                    {
                        return null;
                    }
                }
                else if (cellType == XlCellType.xlCellTypeLastCell)
                {
                    return inputRange;
                }
                else
                {
                    // since inputRange has a single cell, SpecialCells will apply to entire worksheet
                    // this range has all cells from worksheet (UsedRange) of type provided: cellType
                    Range temp = inputRange.SpecialCells(cellType);

                    // intersect range with single cell (inputRange) with above range
                    Range rangeOverlap = Intersect(inputRange, temp);

                    // if range with single cell is contained in that intersection, then this cell is of type xlCellTypeConstants
                    if (rangeOverlap.Count == inputRange.Count && rangeOverlap.Rows.Count == inputRange.Rows.Count && rangeOverlap.Columns.Count == inputRange.Columns.Count)
                    {
                        return inputRange;
                    }
                    else
                    {
                        return null;
                    }
                }
            }
            else
            {
                return inputRange.SpecialCells(cellType);
            }
        }
        catch (System.Runtime.InteropServices.COMException ex)
        {
            return null;
        }
    }


    /// <summary>
    /// <para>Customized function for intersection of two ranges (<paramref name="rangeA"/> ∩ <paramref name="rangeB"/>)</para>
    /// </summary>
    /// <param name="rangeA"></param>
    /// <param name="rangeB"></param>
    /// <returns>Range corresponding to intersection of the two provided ranges</returns>
    /// <remarks>This function returns null if any of provided ranges is null or malformed, unlike Application.Intersect which throws exception</remarks>
    public static Range Intersect(Range rangeA, Range rangeB)
    {
        Range rngIntersect;
        if (rangeA == null)
        {
            rngIntersect = null;
        }
        else if (rangeB == null)
        {
            rngIntersect = null;
        }
        else if (rangeA.Worksheet != rangeB.Worksheet)
        {
            rngIntersect = null;
        }
        else
        {
            try
            {
                rngIntersect = Globals.ThisAddIn.Application.Intersect(rangeA, rangeB);
            }
            catch (Exception ex)
            {
                rngIntersect = null;
            }
        }

        return rngIntersect;
    }