Conditional formatting with VBA formula not persisting

I'm using Excel 2007 and I have a VBA module added to my project

Function RegEx(Value As String, Pattern As String, Optional IgnoreCase As Boolean = False)
    Dim r As New VBScript_RegExp_55.RegExp
    r.Pattern = Pattern
    r.IgnoreCase = IgnoreCase
    If r.Test(Value) Then
        RegEx = 1
    Else
        RegEx = 0
    End If
End Function

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Code references, Microsoft VBScript Regular Expressions 5.5

Using this I added conditional formatting to a whole column. Using the formula option and selecting to fill red when true;

Formula for conditional formatting

=NOT(RegEx(CELL("contents"),"^[A-Za-z0-9 ]{0,20}$"))

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When I type a in a cell that's conditionally formatted, a value that would cause the formula to return true ie. "&" and hit Enter or Tab I see the field flase red but return to no formatting. If I edit the field either with a mouse click or F2 and hit Esc, the red formatting is persistent.

Example:

i think the VBA and Excel formula are correct since the formatting stays when I hit escape, but how can I get it to be formatted if a user presses Enter or Tab.  

Edit: it may be the excel formula part

CELL("contents")

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How do I reference the value of the cell being evaluated?