External references changed when sheet is closed

[crctetley]

[FONT=&quot]I have two spreadsheets stored in the same folder on OneDrive. Values in Tab1 on Filename1 is referenced by Filename2.
Filename2 contains formulae like:
=IF(ISBLANK('[Filename1.xlsx]Tab1'!A1),"",('[Filename1.xlsx]Tab1'!A1))
and this produces the desired result.
However, when I close and reopen Filename2, there is a series of alerts:
This workbook contains links to one or more external sources that could be unsafe. If you trust the links, update them to get the latest data. Then Don't Update or Update
then
Alert
Sorry we couldn't find 'https://d.docs.live.net/Users/Chris/OneDrive/Spreadsheets/Filename1.xlsx '.
Is it possible it was moved or deleted?

and finally
Microsoft Excel cannot access the file 'https://d.docs.live.net/Users/Chris/OneDrive/Spreadsheets/Filename1.xlsx'. There are several possible reasons.
When I finally open Filename2, I find that all the formulae have changed to something like:
=IF(ISBLANK('https://d.docs.live.net/Users/Chris/OneDrive/Spreadsheets/[Filename1.xlsx]Tab1'!A1),"",('https://d.docs.live.net/Users/Chris/OneDrive/Spreadsheets/[Filename1.xlsx]Tab1'!A1))
This was all working properly until quite recently.
What is making the formulae change, and how can I avoid it?


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