Debug.Print shows me a value, but 'If not' wouldn't work with this value

Debug.Print shows me a value, but 'If not' wouldn't work with this value

I am totally baffled. Can't find a solution. I ask for the value of a shape:
? ActiveWindow.Selection.ShapeRange.TextFrame.MarginBottom
Answer: 11.29354
I write a routine:
If Not oshp.TextFrame.MarginBottom = 11.29354 Then
TellMe = "MarginBottom =" & oshp.TextFrame.MarginBottom & " but not
11.29354"
End If
The routine won't work. I claims the shape's MarginBottom has not the
value, but in the same moment it gives me the value as a result.
That would mean the value is not the value. Any experienced guy has
background info on this?