title: Why is Excel re-executing functions in the same and different workbook when I create a new UDF and assign it to a cell?
body: <p>I have two workbooks open.
  In workbook A I have some UDFs assigned to cells and in workbook B I have some UDFs assigned to cells.  These have already been executed, so the cells have values. 
  In workbook B (i.e. in the VBE) I create a new UDF, call it bar:</p>
  
  <pre><code>Function bar()
      bar = "bar"
  End Function
  </code></pre>
  
  <p>When I then go into Excel and assign bar() to a cell in workbook B (with <code>=bar()</code>) and then hit Enter, the UDFs in both the same workbook and in the other open workbook (workbook A) are triggered. They are re-executed, despite already having been executed and the cells having been populated with values. </p>
  
  <p>Why is this?  It's bizarre and very annoying behaviour even in my tiny little practice workbooks.  What if I had 100 UDFs in a workbook? As soon as I add a new UDF and assign it to a cell, all the UDFs would be triggered. </p>
  
  <p>I am using Excel 2016. Thanks in advance. </p>