SpecialCells(xlCellTypeVisible) not working in UDF

Question

Based on the question posed by @Chips Ahoy, I decided to create a UDF to find the PercentRank of visible cells in a range.

While @Chips seems happy with my syntax correction, I am actually unable to get my UDF to work correctly.

When I run the below, the two addresses output read identical. In my example using a formula of =VisiblePercentRank($A$2:$A$41,0.5) , both addresses output to the immediate window read $A$2:$A$41, despite rows 3 to 11 being hidden by an autofilter.

Code:

Function VisiblePercentRank(x As Range, RankVal As Double)
    Debug.Print x.Address, x.Rows.SpecialCells(xlCellTypeVisible).Address
    VisiblePercentRank = WorksheetFunction.PercentRank(x.Rows.SpecialCells(xlCellTypeVisible), RankVal)
End Function

Also tried removing .Rows:

Function VisiblePercentRank(x As Range, RankVal As Double)
    Debug.Print x.Address, x.SpecialCells(xlCellTypeVisible).Address
    VisiblePercentRank = WorksheetFunction.PercentRank(x.SpecialCells(xlCellTypeVisible), RankVal)
End Function

Should the second output not read $A$2,$A$12:$A$41 or have I missed something?

Using Excel/Office 2013, 64bit on Win7, 64bit.

BRAIN FRYING UPDATE

I have found that my UDF works if I run it from the immediate window:

?VisiblePercentRank(range("A2:A41"),0.5)
$A$2:$A$41    $A$2:$A$11,$A$39:$A$41
 0.207 

But if run from an in-cell formula of =VisiblePercentRank(A2:A41,0.5):

$A$2:$A$41    $A$2:$A$41

Answer 1

It seems that SpecialCells is known to fail in UDFs. A few sources: 1, 2, 3

You'd have to create your own function. Perhaps something like this:

Function VisiblePercentRank(x As Range, RankVal As Double)
    Debug.Print x.Address, VisibleCells(x).Address
    VisiblePercentRank = WorksheetFunction.PercentRank(VisibleCells(x), RankVal)
End Function

Private Function VisibleCells(rng As Range) As Range
    Dim r As Range
    For Each r In rng
        If r.EntireRow.Hidden = False Then
            If VisibleCells Is Nothing Then
                Set VisibleCells = r
            Else
                Set VisibleCells = Union(VisibleCells, r)
            End If
        End If
    Next r
End Function