Editing XLA/XLAM Add-ins

[excel_user_a]

Hello Mr. Excel Community,

I have experienced the following problem using Excel 2007 under Windows XP.
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I have a VBA library (library.xlam) that is used by a client Excel app (client.xlsm), both stored in a folder PROD. By "used" I mean that the client references the library (in VBA editor, under References, there is a link to the library).
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I copy the library and then the app into another folder DEV (in that sequence). Let's call these library1.xlam and client1.xlsm.
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I edited library1.xlam and tried to save it into DEV, but got error preventing saving.
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After rooting around for the cause, I noticed that client.xlsm NOW REFERENCES THE DEV VERSION OF THE LIBRARY (by looking in the References under VBA editor).
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Why does copying a library cause a client to reference the copy? What are the rules governing this behavior? I don't think this happens all the time - we have seen this behavior a few times, but for the most part I believe I have performed a sequence very much like that above with no problem. Does the order of copying the files matter? Does the method of copying the files matter?
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Cutting to the chase: what is the recommended way of generating a development version of a library without affecting any clients of that library?